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Vegetative  Vigor  of  the  Host  as  a  Factor  Influencing 

Susceptibility  and  Resistance  to  Certain  Rust 

Diseases  of  the  Higher  Plants 


BY 

MORRIS  ABEL  RAINES 


A  DISSERTATION  SUBMITTED  IN  PARTIAL  FULFILLMENT  OF  THE  REQUIRE- 
MENTS FOR  THE  DEGREE  OF  DOCTOR  OF  PHILOSOPHY,  IN  THE  FACULTY 
OF  PURE  SCIENCE,  COLUMBIA  UNIVERSITY. 


Reprinted  from  the 

AMERICAN  JOURNAL  OF  BOTANY,  Vol.  IX,  No.  4,  pp.  183-203, 
April,  1922,  and  No.  5*  pp.  215-238,  May,  1922. 


Vegetative  Vigor  of  the  Host  as  a  Factor  Influencing 

Susceptibility  and  Resistance  to  Certain  Rust 

Diseases  of  the  Higher  Plants 


BY 

MORRIS  ABEL  RAINES 


A  DISSERTATION  SUBMITTED  IN  PARTIAL  FULFILLMENT  OF  THE  REQUIRE- 
MENTS FOR  THE  DEGREE  OF  DOCTOR  OF  PHILOSOPHY,  IN  THE  FACULTY 
OF  PURE  SCIENCE,  COLUMBIA  UNIVERSITY. 


Reprinted  from  the 

AMERICAN  JOURNAL  OF  BOTANY,  Vol.  IX,  No.  4,  pp.  183-203, 
April,  1922,  and  No.  5,  pp.  215-238,  May,  1922. 


[Reprinted  from  the  AMERICAN  JOURNAL  OF  BOTANY  9:  183-203,  April,  1922.] 


VEGETATIVE  VIGOR  OF  THE  HOST  AS  A  FACTOR  INFLU- 
ENCING SUSCEPTIBILITY  AND  RESISTANCE  TO 
CERTAIN  RUST  DISEASES  OF  THE  HIGHER 
PLANTS' 

i 

M.  A.  RAINES 
(Received  for  publication  July  13,  1921) 

INTRODUCTION 

Studies  on  the  cereal  rusts  were  made  covering  various  phases  of  the 
phenomena  of  rust  epidemiology,  including  the  effects  of  season,  age  of  the 
host  plant,  etc.,  on  its  susceptibility  and  on  the  virulence  of  the  disease; 
effects  of  varying  dosage  in  securing  inoculation;  effects  of  the  general 
nutritional  condition  of  the  host,  etc.  In  carrying  out  these  studies  I  have 
had  the  opportunity  to  convince  myself  of  the  frequently  observed  fact  that 
health  and  vigor  of  the  host  favor  rather  than  hinder  its  inoculation  by  a 
rust  and  the  further  development  of  the  diseased  condition.  This  observa- 
tion has  frequently  been  made  and  more  or  less  casually  reported  in  the 
literature  on  the  rusts  and  other  fungous  diseases  of  plants.  The  significance 
of  such  observations  in  relation  to  general  theories  of  immunity  and  resis- 
tance to  disease  has,  however,  nowhere  been  adequately  recognized,  and 
I  have  thought  it  worth  while  to  bring  together  the  available  evidence 
bearing  on  this  point. 

It  is  a  commonplace  of  pathological  theory  that  the  health  and  vigor  of 
an  organism  and  its  susceptibility  to  disease  are  antithetic  variables,  that 
as  one  increases  or  is  increased  the  other  diminishes  or  is  diminished  corre- 
spondingly. Adami  (1910, A  i:  409),  summarizing  the  subject  of  predis- 
position to  disease,  lists  the  causes  of  acquired  susceptibility  as  (i)  social 
and  environmental  conditions;  (2)  injury;  (3)  malnutrition;  (4)  previous 
attack  of  the  same  disease  or  other  infectious  disease;  and  (5)  exhaustion; 
all  of  them  factors  diminishing  the  vitality  of  the  host.  Zinnser  (1914, 
p.  59),  discussing  the  broader  principles  of  infection  and  resistance,  states: 

A  person  suffering  from  functional  impairment  of  any  kind  is  more  likely  to  permit  the 
invasion  of  a  pathogenic  microorganism  than  is  a  perfectly  healthy  well-nourished  indi- 
vidual of  the  same  species. 

Kolmer  (1917,  p.  101)  says,  similarly: 

Acquired  susceptibility  .  .  .  may  be  due  to  various  factors,  most  of  which  lead  to  a 
state  of  reduced  vitality,  normal  physiologic  processes  being  impaired  to  a  greater  or  less 
degree. 

1  The  list  of  literature  cited  will  be  found  at  the  conclusion  of  the  second  paper  of 
this  series. 


1 84  AMERICAN   JOURNAL   OF    BOTANY  [Vol.   9 

Among  plant  pathologists,  Jones  (1905,  p.  23)  writes: 

Disease  resistance  and  vegetative  vigor  are  closely  associated,  although  the  factors 
involved  are  not  necessarily  identical.  ...  So  far  as  the  evidence  goes  it  seems  to  suggest 
that  high  vegetative  vigor  enables  the  plant  to  ward  off  in  some  degree  the  fungus  attack. 

In  direct  contrast  with  this  view  it  must  be  noted  that  workers  in  the 
field  of  the  rust  diseases  of  higher  plants  have  on  several  occasions  been 
prompted  to  generalize  to  directly  the  opposite  effect — that  they  found  host 
vigor  and  susceptibility  to  disease  not  antithetic,  and  not  independent,  but 
parallel  variables.  Arthur  (1903,  p.  13),  in  a  presidential  address  before 
the  Botanical  Society  of  America,  stated  from  his  long  experience  with 
plant  rusts  that 

So  intimate  is  the  association  of  parasite  and  host  that  as  a  rule  the  vigor  of  the  parasite 
is  directly  proportional  to  the  vigor  of  the  host.  Every  culturist  soon  learns  that  to  have 
success  in  his  work  he  must  employ  strong,  rapidly  growing  plants.  Even  if  he  succeeds  in 
infecting  weak  plants,  the  fungus  will  rarely  come  to  satisfactory  fruitage. 

Sheldon  (1903,  p.  74),  summarizing  his  illuminating  studies  on  the 
asparagus  rust,  concludes: 

Lowered  vitality  does  not  favor  infection.  .  .  .  Whatever  affects  the  growth  of  the 
asparagus  has  a  like  effect  on  the  rust. 

Stakman,  in  his  extensive  studies  on  the  cereal  rusts,  on  several  occasions 
expresses  similar  views.  Thus  (1914,  p.  40)  he  concludes  that 

These  experiments  show  that  whatever  is  conducive  to  the  vigorous  development  of 
the  host  is  ordinarily  conducive  to  the  vigorous  development  of  the  parasite  also. 

And  in  another  place  (Stakman  and  Levine,  1919,  pp.  75  and  76): 

Deficiency  of  soil  moisture  and  sunlight  and  other  ecological  factors  affecting  the  host 
plant  unfavorably  appear  to  be  equally  unfavorable  to  the  rust  parasite.  .  .  .  Adverse 
environmental  conditions  unfavorable  to  the  host  are  also  unfavorable  for  the  parasite, 
affecting  the  virulence  and  spore  size  of  the  latter. 

While  the  authors  make  their  point  incidentally  and  in  no  instance  dis- 
cuss their  findings  from  the  point  of  view  of  the  general  question  of  the 
relation  between  host  vigor  and  susceptibility  in  -infectious  disease,  it  is 
evident  that  the  question  is  suggested  as  to  the  possibly  special  and,  from 
the  point  of  view  of  the  relation  observed  in  the  larger  number  of  infectious 
diseases  of  plants  and  animals,  peculiar  relation  between  vegetative  vigor 
of  the  host  and  susceptibility  to  infection  in  the  rust  diseases  of  the  higher 
plants.  The  demonstration  of  such  a  peculiar  relation  would  be  of  the- 
oretical interest  as  limiting  and  qualifying  the  universality  of  the  commonly 
accepted  dictum  that  host  vigor  and  virulence  of  disease  are  in  inverse 
relation  and  would  be  of  profound  import  in  defining  the  practical  problem 
of  the  prevention  and  control  of  the  diseases  concerned. 


Apr.,  1922]  RAINES—   VEGETATIVE    VIGOR   OF   THE    HOST  185 

REVIEW  OF  LITERATURE 

Physiological  studies  on  the  rusts  have  been  reported  almost  entirely 
from  the  point  of  view  of  a  direct  relation  between  the  environmental  factor 
'  concerned  and  the  rust  fungus,  the  essential  intermediary  between  the  two, 
the  host,  being  kept  more  or  less  indistinctly  in  the  background.-  A  marshal- 
ing of  the  available  data  on  the  physiology  of  the  rusts  from  the  point  of 
view  of  the  present  study,  the  possible  correlation  between  host  vigor  and 
virulence  of  the  parasite,  reveals  a  very  general  agreement  in  favor  of  the 
concept  that  in  the  rust  diseases  of  the  higher  plants  there  is  a  tendency  for 
the  parasite  to  exhibit  a  higher  incidence  of  infection  and  greater  virulence 
on  the  host  of  greater  vegetative  vigor.  Similar  instances  in  other  classes 
of  plant  diseases  are  cited  in  the  general  discussion. 

Host  Nutrition :  Nitrogen  Nutrition  and  Mineral  Nutrients 

Field  Studies 

Butler  (1918,  p.  73)  describes  the  coffee  leaf  disease  (Hemileia  vastatrix 
B.  &  Br.)  as  having  first  appeared  on  some  of  the  best  coffee  in  Ceylon,  and 
states  that  it  is,  in  the  case  of  this  disease,  considered  as  established  that 
fungous  infection  and  growth  occur  better  in  strong  leaves,  rich  in  nutriment, 
than  in  those  with  less  food  supply. 

The  greater  susceptibility  to  rust  of  wheat  grown  on  highly  fertile  land 
has  been  noted  repeatedly.  Little  (1883,  p.  634)  states  that  high  manuring, 
especially  with  nitrogenous  manures,  predisposes  wheat  plants  to  rust. 
And  Bolley  (1889,  p.  17)  writes  that 

It  is  a  matter  of  common  note  that  soils  rich  in  organic  plant  foods,  such  as  low-lying 
loams,  are  quite  liable  to  produce  rusted  crops;  and  in  England,  where  great  quantities  of 
nitrogenous  fertilizers  are  used,  much  has  been  said  as  to  the  liability  of  the  crop  to  rust 
upon  fields  to  which  such  manures  have  been  applied.  Such  observations  go  to  confirm 
the  belief  that  soils  excessively  rich  in  nitrogen,  either  natural  or  applied,  produce  wheat 
easily  attacked  by  rust. 

Freeman  and  Johnson  (1911,  p.  69),  in  their  general  review  of  the  cereal 
rust  problem  in  the  United  States,  state: 

...  It  is  now  well  established  that  where  there  is  an  excess  of  nitrogen  in  the  soil, 
other  things  being  equal,  grains  are  more  severely  attacked  by  rust  than  crops  on  soil  con- 
taining less  nitrogen.  .  .  .  Where  barnyard  manures  have  been  applied  heavily  the  result 
is  similar,  and  where  grains  are  grown  after  a  crop  of  clover,  beans,  or  vetch,  rusts  may  be 
expected.  In  fact  it  may  be  generally  stated  that  where  soils  are  rich  in  nitrogen,  pro- 
ducing rank  and  succulent  plant  growth,  rust  attacks  will,  as  a  rule,  be  most  severe  on 
account  of  increased  succulence  of  the  plants,  increased  rankness  of  growth,  delay  in  drying 
out  after  showers  and  dews,  and  slight  delay  in  the  ripening  period.  On  the  other  hand 
phosphate  of  lime  tends  to  shorten  the  ripening  period  and  thus  acts  as  a  rust  preventive 
to  some  extent.  ...  In  general,  a  rust  attack  is  most  virulent  on  a  healthy  plant. 

Peacock  (1911)  states  that  rust  in  wheat  and  oats  is  favored  by  pre- 


1 86 


AMERICAN  JOURNAL  OF   BOTANY 


[Vol.  9. 


disposition  due  to  a  too  vigorous  growth  in  early  life.  Biffen  (1912),  in  his 
studies  on  the  inheritance  in  wheat  of  rust  resistance  to  Puccinia  ghimarum, 
found  that  the  rust  is  most  virulent  when  a  complete  fertilizer  is  used,  and 
that  the  virulence  of  the  disease  decreases  with  a  decrease  in  the  amount 
of  fertilizer.  Comparing  the  two  principal  types  of  asparagus  soils  in 
California,  the  sediment  and  the  peat,  Smith  (1905,  p.  56)  notes  that  aspar- 
agus growing  in  the  latter  soil  is  considerably  more  damaged  by  the  same 
amount  of  disease.  He  comments  that  on  peat  formations,  composed 
almost  entirely  of  vegetable  matter  and  water,  a  very  luxuriant,  quick- 
growing,  tender,  and  succulent  asparagus  is  produced. 

Zavitz  (1913)  reports  some  very  interesting  observations  on  the  relative 
susceptibility  to  rust  of  oats  grown  under  conditions  of  varying  thickness 
of  seeding.  The  experiment  was  conducted  through  each  of  four  years, 
using  both  large  and  small  seed  of  heavy-stooling,  medium-stooling,  and 
light-stooling  varieties  of  oats,  and  planting  the  seed  of  each  variety  in 
squares  one,  two,  three,  four,  six,  eight,  and  twelve  inches  apart.  Table  I 
is  adapted  from  the  data  presented  by  Zavitz,  and  presents  the  average 
results  of  thirty-two  tests  made  by  planting  oats  at  seven  different  distances 
apart.  The  results  are  the  averages  for  four  years. 

TABLE  i 


Inches 

Number   of 

Height 

5£ 

Days 

Relative  Yield 

per  Plant 

Per- 

between 
Plants 

Heads  per 
Plant 

in 
Inches 

centage 
Lodged 

to 
Mature 

Straw 

Grain 

centage 
Rusted 

I 

1.0 

20.4 

5-6 

91 

100 

100 

II.  8 

2 

I.I 

27.8 

11.9 

93 

361 

457 

15.0 

3 

1.3 

32.6 

12.8 

94 

782 

1,227 

17.8 

4 

2.0 

33-i 

29.9 

95 

1,179 

2,031 

20.9 

6 

4-2 

35-3 

35-8 

97 

2,823 

4,402 

254 

8 

6-5 

34-9             34-7 

99 

4,389 

6,645 

27.7 

12 

II.  2 

34-9 

30.1 

100 

8,475 

10,320 

33-2 

The  greater  amount  of  rust  observed  with  the  increased  distance  between 
plants  is  best  correlated  with  the  increased  luxuriance  of  growth  exhibited 
by  these  plants.  The  difference  of  a  week  in  the  time  of  maturing  between 
the  most  closely  spaced  and  the  most  liberally  spaced  oat  plants  is  hardly 
sufficient  to  account  for  the  difference  in  the  amount  of  rust  infection. 
Observations  were  made  at  frequent  intervals  through  the  summer,  and 
a  rust  difference  due  only  to  difference  in  time  of  maturity  would  not  have 
shown  up  in  this  fashion  in  the  data.  A  more  logical  explanation  is  the 
increase  in  the  amount  of  lodging  which  closely  parallels  the  increase  in 
percentage  of  rust  from  the  one-inch  spacing  to  the  six-inch  spacing.  But 
from  the  six-inch  spacing  to  the  twelve-inch  spacing  the  amount  of  lodging 
decreases  appreciably  while  the  percentage  of  rust  increases  further,  indicat- 
ing that  the  increase  in  the  amount  of  rust  is  independent  of  lodging.  There 


Apr.,  1922]  RAINES  —  VEGETATIVE   VIGOR   OF   THE   HOST  187 

is  the  strong  suggestion,  therefore,  in  Zavitz's  data  that  the  increase  noted 
in  the  amount  of  rust  present  on  oat  plants  grown  at  progressively  greater 
distances  apart  is  correlated  with  the  increased  luxuriance  of  growth  of  the 
host  plants. 

Water- Culture  and  Sand- Culture  Studies  . 

Ward  (19020)  details  two  experiments  on  the  susceptibility  to  rust  in- 
fection of  host  plants  which  had  been  starved  of  essential  nutrients.  In 
the  first  experiment,  54  young  seedlings  of  Bromus  secalinus  were  used. 
The  plants  were  grown  in  sand  in  14  glass  beakers,  four  to  seven  plants  to 
a  beaker,  and  watered  with  solutions  -of  varying  nutritive  value.  The 
plants  in  one  beaker  received  only  distilled  water.  The  plants  in  another 
beaker  received  a  cold-water  extract  of  fresh  horse  dung,  as  a  solution  of 
high  nutritive  value.  In  a  third  beaker  the  plants  received  a  full  mineral 
nutritive  solution  (described  as  a  "normal  nutritive  mineral  solution  con- 
taining nitrates,  phosphates,  and  sulphates  of  potassium,  calcium,  and 
magnesium").  The  remaining  eleven  beakers  received  an  incomplete 
nutrient  solution,  the  elements  omitted  being  respectively  K;  N;  Mg;  Ca; 
P;  Fe;  N  and  Fe;  Mg  and  Fe;  Ca  and  Fe;  P  and  Fe.  Inoculation  was 
effected  by  applying  uredospores  of  Puccinia  dispersa  to  the  leaves  by  means 
of  a  swab  of  cotton;  at  the  time  of  inoculation  the  seedlings  were  16  days 
old,  counting  from  the  time  of  sowing. 

Ward  records  detailed  observations  on  the  stature,  robustness,  color, 
and  number  of  leaves  of  the  seedlings  in  each  beaker;  on  the  time  of  appear- 
ance, number,  and  size  of  the  pustules  developed  on  them,  and  on  the 
relative  number  of  spores  produced.  Comparing  the  twelve  seedlings 
which  showed  the  most  vigorous  growth  (6  which  received  the  extract  of 
horse  dung,  3  the  full  nutrient  solution,  and  3  the  full  nutrient  solution 
minus  Fe,  the  plants  averaging  20  cm.  in  height)  with  the  ten  poorest  plants 
(4  receiving  distilled  water,  3  the  full  nutrient  solution  minus  N,  and  3  the 
nutrient  solution  minus  N  and  Fe,  the  plants  averaging  II  cm.  in  height), 
the  observations  recorded  by  Ward  indicate  that  in  the  plants  suffering 
from  malnutrition  (i)  the  incubation  period  of  the  rust  was  lengthened  by 
one  and  two  days;  (2)  the  rust  pustules  were  much  smaller  and  produced 
fewer  spores.  In  other  words,  a  starved  host  meant  a  starved  parasite. 
There  is  also  the  suggestion  in  the  data  that  the  starved  seedlings  showed 
a  lower  incidence  of  infection;  but  the  small  number  of  variables  worked 
with,  together  with  the  large  irregularity  in  dosage  inherent  in  the  method  of 
inoculation  used,  compel  reserve  in  making  this  deduction. 

A  second  experiment  with  64  seedlings,  duplicating  the  first,  gave 
similar  results.  Regarding  the  spores  produced  on  well  nourished  and  on 
starved  seedlings,  Ward  states  that  microscopic  examination  revealed  no 
differences.  Spores  from  starved  seedlings  could  produce  infection  on 
other  seedlings,  similarly  starved. 


1 88  AMERICAN   JOURNAL  OF   BOTANY  [Vol.  9, 

In  1905,  Ward  reports  experiments  indicating  that  starving  the  host 
tissue  after  infection  has  taken  place  has  an  adverse  effect  on  the  growth 
of  the  fungous  mycelium.  He  cut  off  infected  leaves  of  cereals  on  the  third 
day  after  artificial  inoculation  and  floated  them  on  water.  Histological 
examinations  of  the  leaves  indicated  that  the  rust  fungus  in  the  tissues 
continued  to  grow  for  a  time,  but  soon  showed  signs  of  starvation. 

Spinks  (1913,  p.  238)  describes  an  experiment  on  the  susceptibility  to 
Puccinia  glumarum  of  wheat  plants  grown  in  water  cultures.  He  used  six 
plants  grown  in  each  of  three  solutions:  a  standard  nutrient  solution  (Det- 
mer's) ;  a  nutrient  solution  containing  four  times  the  quantity  of  ammonium 
phosphate;  and  a  nutrient  solution  containing  four  times  the  quantity  of 
potassium  chloride.  The  cultures  were  inoculated  by  applying  uredospores 
to  the  leaves;  they  were  then  set  outdoors,  so  that  further  spread  of  the 
rust  occurred  naturally.  Spinks  gives  no  data  on  the  condition  of  the 
plants,  and  this  can  only  be  inferred  from  the  mode  of  treatment  they  re- 
ceived. The  data  presented  indicate  that  the  plants  growing  in  the  nutrient 
solutions  containing  a  four-fold  concentration  of  nitrogen  were  more  sus- 
ceptible than  those  in  the  standard  solution.  Excess  concentration  of 
KC1  gave  an  apparent  slight  depression  of  susceptibility. 

Stakman  (1914,  p.  39)  reports  some  experiments  with  Puccinia  graminis 
tritici  on  wheat  seedlings  grown  in  water  cultures.  In  an  experiment  in 
which  nitrogen  and  phosphorus  were  omitted  from  the  culture  solutions, 
the  check  plants  were  more  severely  attacked  than  the  experimental  plants. 
Summarizing  his  results,  Stakman  says  (p.  48) : 

It  was  found  that  in  general  the  absence  or  presence  in  excessive  amounts  of  various 
nutrient  substances,  such  as  nitrogen  and  phosphorus  salts,  did  not  directly  affect  the 
immunity  or  susceptibility  of  wheats.  Conditions  favoring  a  normal  development  of  the 
host  were  conducive  to  a  vigorous  development  of  the  rust.  The  action  of  fertilizers,  either 
natural  or  artificial,  is  probably  indirect. 

Soil-Culture  Experiments 

Sheldon  (1905,  p.  226)  remarks  on  the  low  susceptibility  shown  by 
poorly  growing  carnations  to  artificial  infection  with  Puccinia  Caryophylli: 

The  results  show  that  the  plants  that  were  making  a  vigorous  growth  were  more  sus- 
ceptible to  artificial  infection  than  those  that  were  making  little  or  no  apparent  growth. 
A  few  slowly  growing  plants  were  repeatedly  inoculated  without  success  until  the  plants 
were  given  extra  care  and  stimulated  so  that  they  began  to  grow  more  vigorously.  Some 
carnations,  grown  in  small  pots,  were  each  inoculated  five  or  six  times  at  intervals  of  about 
twenty  days  without  any  of  the  inoculations  being  effective.  These  plants  grew  very 
slowly,  were  slender,  and  produced  only  one,  or  at  most  two,  small  blossoms. 

In  the  same  paper  (p.  228)  Sheldon  reports  an  experiment  on  the  length 
of  the  incubation  period  of  the  carnation  rust  in  which  he  inoculated  simulta- 
neously 170  pinks  growing  in  soils  of  varying  nutritive  values.  The  plants 
had  been  derived  by  taking  sets  of  cuttings  from  the  same  stock  plant,  a 


Apr.,  1922]  RAINES—  VEGETATIVE   VIGOR   OF   THE   HOST  189 

green-leaved  pink  known  to  be  very  susceptible  to  carnation  rust,  and  they 
were  grown  in  five  different  soils  ranging  in  composition  from  one  that  was 
principally  sand  to  one  containing  chiefly  organic  matter.  Sheldon's  ob- 
servations indicated  that  the  growth  of  the  host  varied  directly  with  the 
amount  of  organic  matter,  nitrogen,  and  silt  in  the  different-soils ;  and  that 
with  increasec}  vigor  and  growth  of  the  host  the  incubation  period  of  the 
fungus  decreased  in  length,  from  21  days  in  the  poorest  plants  to  16  days 
in  the  most  vigorous  individuals. 

Miss  Gibson  (1904,  p.  188)  describes  an  experiment  on  the  effects  of 
nutritional  treatment  on  the  susceptibility  ol  certain  varieties  of  chrysan- 
themum to  rust. 

The  young  plants  were  then  divided  into  four  groups.  A  were  fed  as  if  for  exhibition ; 
B  were  grown  normally;  C  were  starved  by  being  grown  in  small  pots;  and  D  were  grown  in 
a  warm  greenhouse. 

The  rust  developed  on  all  the  plants,  but  a  luxuriant  state  of  growth  of 
the  host  favored  the  greater  development  of  the  fungous  mycelium. 

Spinks  (1913,  p.  240)  conducted  an  experiment  on  the  susceptibility 
to  rust  of  wheat  plants  grown  in  pots  receiving  different  nutritive  solutions. 
The  data  indicate  somewhat  higher  susceptibility  on  the  part  of  the  plants 
richly  fed  with  nitrogen.  Stakman  (1914,  p.  16)  finds  that  high  fertilization 
of  the  soil  increased  the  susceptibility  to  infection  by  Puccinia  graminis 
tritici  of  resistant  varieties  of  wheat,  and  so  concludes  that  high  fertilization 
is  conducive  to  increased  severity  of  rust  attack  on  very  resistant  varieties 
as  well  as  on  susceptible  forms. 

Indicating  that  the  effect  of  specific  nutrient  substances  is  indirect, 
secondary  to  their  effect  on  the  vigor  of  the  host,  is  the  observation  by 
Stakman  and  Levine  (1919,  p.  72)  that  an  application  of  sodium  nitrate, 
excessive  to  the  point  of  inhibiting  the  growth  of  the  host,  also  inhibits  the 
development  of  the  rust  and  diminishes  very  perceptibly  the  size  of  the 
urediniospores.  Ward  (i9O2a)  states  that  the  size  of  the  uredospores  was 
not  affected  by  starving  the  host.  Stakman  and  Levine  arrived  at  their 
observation  that  the  size  of  the  spores  is  affected  by  biometrical  methods, 
which  would  cause  to  stand  out  distinctly  size  differences  not  apparent  on 
gross  examination.  Ward  does  not  give  any  spore  measurements. 

Host  Nutrition:  Carbon  Metabolism 

Intimate  relation  between  the  progress  of  a  rust  infection  and  the 
carbon  metabolism  of  the  host  tissue  has  been  demonstrated  by  Ward 
(1905),  Fromme  (1913),  and  Mains  (1917).  Sheldon  (1903)  studied  the 
effect  of  light  and  temperature  on  rust  development,  and  Stakman  and  his 
co-workers  (1917,  1919)  have  studied  quantitatively  the  effects  of  light  on 
the  cereal  rusts. 

Ward  (1905,  p.  40)  refers  to  experiments  on  cereal  rusts  indicating  that 


AMERICAN   JOURNAL  OF   BOTANY  [Vol.  9, 

when,  shortly  after  inoculation,  the  host  is  placed  under  conditions  where 
it  cannot  manufacture  carbohydrates,  as  by  keeping  it  in  the  dark  or  in 
light  from  which  the  red-orange  end  of  the  spectrum  is  filtered  off  or  in  air 
deprived  of  carbon  dioxide,  the  development  of  the  rust  is  inhibited. 

Fromme  (1913,  p.  516)  found  that  placing  oat  plants  recently  inoculated 
with  Puccinia  coronifera  in  the  dark  for  a  period  of  several  days  increased 
the  length  of  the  incubation  peiiod  of  the  rust  by  a  corresponding  interval. 
Fromme  interprets  the  observation  to  indicate  that  the  fungus  is  dependent 
for  its  nutrition  on  some  intermediate  product  of  photosynthesis. 

Mains  (1917,  p.  191)  confirms  Fromme's  observation  that  the  develop- 
ment of  the  crown  rust  of  oats  is  retarded  in  the  absence  of  light,  and  adds 
that  if  the  infected  plant  is  left  in  the  dark  too  long  (which  would  greatly 
impair  the  vitality  and  vigor  of  the  host  tissue)  the  rust  is  killed.  Mains 
also  independently  repeated  Ward's  observation  that  growing  the  host 
plants  in  an  atmosphere  free  from  carbon  dioxide  inhibits  the  development 
of  the  rust.  Similar  experiments  with  Puccinia  Sorglii  on  seedling  plants  of 
Zea  Mays,  however,  failed  to  arrest  the  development  of  the  rust.  Further 
experiments  showed  that  if  the  host  leaf  is  supplied  with  carbohydrates, 
either  from  the  reserve  stores  of  the  endosperm  or  by  being  floated  under 
aseptic  conditions  on  a  sugar  solution,  then  the  rust  develops  successfully, 
even  if,  because  of  the  absence  of  light  or  of  carbon  dioxide,  the  host  tissue 
cannot  manufacture  its  own  carbohydrates.  Mains  is  therefore  prompted 
to  qualify  Fromme's  inference  that  the  rust  is  dependent  upon  intermediate 
products  of  photosynthesis  into  the  statement  that  the  rust  is  dependent 
upon  transitory  carbohydrates. 

It  does  not  necessarily  follow  from  an  observation  that  the  development 
of  the  rust  is  inhibited  upon  a  plant  starved  of  an  essential  nutrient— 
whether  carbon,  or  nitrogen,  or  potassium,  etc. — that  the  rust  fungus  is 
dependent  for  its  nutrition  upon  compounds  of  that  substance.  As  long 
as  the  host  plant  is  at  all  alive,  or,  even  if  it  is  dead,  before  disintegration 
of  its  substance  has  set  in,  it  contains  carbon,  nitrogen,  etc.,  compounds, 
and  we  cannot  say  that  the  rust  could  not  develop  because  of  the  absence  of 
such  compounds.  Such  observations  are  best  interpreted  on  the  basis  of 
the  physiological  condition  of  the  host  when  it  is  starved  of  an  essential 
nutrient  substance.  We  can  not  say  that  a  host  plant  starved  of  an  essential 
nutrient  is  a  host  plant  deficient  in  that  particular  class  of  substances;  but 
we  can  say  that  a  host  plant  starved  of  an  essential  nutrient  is  a  host  plant 
that  is  not  assimilating,  that  is  not  growing,  a  plant  in  which  anabolic  proc- 
esses are  at  a  standstill  and  katabolic  processes  predominate.  And  we 
are  justified  in  inferring  from  the  observed  behavior  of  rust  fungi  on  host 
plants  starved  of  essential  nutrients  that  a  plant  which  is  not  assimilating, 
which  is  not  growing,  in  which  anabolic  processes  are  at  a  standstill  and 
katabolic  processes  predominate*,  does  not  make  a  congenial  host  for  the 
rust  fungus.  The  suggestion  that  the  rust  is  dependent  for  nutrition  upon 


Apr.,  1922]  RAINES  —  VEGETATIVE   VIGOR   OF   THE    HOST  19! 

some  particular  class  of  substances  within  the  host  is  strongest  in  the  case 
of  the  carbon  compounds,  because  of  the  relatively  large  amounts  of  carbon 
needed  by  the  growing  plant  and  because  of  the  facility  and  exactness  with 
which  the  growth  and  vitality  of  the  host  plant  can  be  experimentally  con- 
trolled through  this  phase  of  its  metabolism. 

Stakman  and  his  co-workers  have  studied  the  light  relations  of  Puccinia 
graminis  tritici  inoculated  on  seedling  plants  of  wheat.  Stakman  and 
Piemeisel  (1917,  p.  487)  state  that  a  considerable  amount  of  sunlight  is 
necessary  for  the  best  development  of  the  rust.  They  found  that  during 
periods  of  cloudy  weather  the  incubation  period  may  be  lengthened  a  week 
or  more,  and  that  the  rust  does  not  develop  so  abundantly  as  during  bright 
weather.  Shaded  plants  invariably  were  more  weakly  infected  than  the 
others.  Partially  etiolated  plants  were  infected  with  difficulty,  and  'the 
rust  developed  very  weakly  on  them.  No  rust  developed  on  etiolated 
plants.  Stakman  and  Levine  (1919,  p.  71)  found  that  the  rust  developed 
considerably  better  in  fairly  high  intensities  of  light  than  under  conditions 
of  less  favorable  illumination.  The  size  of  the  urediniospores  responded  in 
a  similar  manner.  They  summarize  their  observations  on  the  light  relations 
of  the  rust  as  indicating  that 

...  In  as  much  as  the  photosynthetic  activities  of  the  host  plant  are  affected  by  the 
light  intensity,  in  so  much  does  the  structure  and  function  of  the  rust  depend  on  the  same 
factor. 

Water  Relations 

While  many  observations  have  been  made  on  the  relation  of  moisture 
conditions  of  soil  and  air  to  rust  virulence  on  plants  in  the  field,  they  are 
subject  to  criticism  in  that  they  do  not  distinguish  between  the  effect  of  the 
moisture  conditions  on  uredospore  germination  and  penetration,  and  the 
effect  on  the  vigor  of  the  host  and  the  progress  of  the  rust  infection  in  its 
tissues.  Abundant  moisture  is  always  favorable  to  uredospore  germination 
and  infection,  but  the  effect  on  the  physiology  of  the  host  is  specific  for  the 
plant.  Abundance  of  moisture  will  favor  the  growth  of  a  mesophyte,  but 
it  will  have  a  depressing  effect  on  the  vigor  of  a  plant  of  xerophytic  tend- 
encies. Limiting  ourselves,  therefore,  to  observations  when  inoculation 
was  artificially  effected  under  conditions  of  maximum  atmospheric  humidity, 
the  evidence  permits  the  inference  that  the  moisture  conditions  of  at- 
mosphere and  soil  most  favorable  for  the  growth  of  the  host  plant  are 
likewise  optimum  for  the  growth  and  sporulation  of  the  rust. 

The  most  complete  and  suggestive  experiment  is  reported  by  Stakman 
(1914,  p.  35).  Wheat  plants  of  both  drought-resisting  varieties  and  or- 
dinary mesophytic  types  were  employed,  and  they  were  grown  in  two  series. 
The  soil  in  one  series  was  kept  very  wet,  while  that  in  the  other  series  was 
kept  as  dry  as  possible  without  endangering  the  life  of  the  plants.  On 
inoculation  with  rust,  the  drought-resisting  forms  exhibited  better  infection 


IQ2  AMERICAN   JOURNAL   OF    BOTANY  [Vol.  9. 

in  the  dry  soil',  while  the  mesophytic  types  showed  slightly  greater  virulence 
of  disease  in  the  moist  soils.  Repeated  trials  were  made  with  substantially 
the  same  result.  Stakman  concludes: 

It  is  probable  then  that,  conditions  having  been  favorable  for  a  rust  infection,  the  water 
relation  in  the  soil  which  is  most  favorable  for  the  host  plant's  development  is  also  the  most 
favorable  for  the  development  of  the  rust. 

Mains  (1917,  p.  189)  found  that  the  development  of  P.  Sorghi  on  corn, 
as  shown  by  the  number  of  pustules  produced,  is  favored  by  a  humid  at- 
mosphere and  by  a  wet  soil — conditions  favorable  to  the  growth  of  the 
corn  plant.  The  length  of  the  incubation  period  was  not  appreciably 
influenced. 

Stakman  and  Levine  (1919,  p.  45),  in  experiments  to  determine  the 
length  of  time  that  wheat  seedlings  inoculated  with  P.  graminis  tritici 
should  be  kept  in  a  saturated  atmosphere  in  order  to  obtain  maximum  in- 
fection, found  that  keeping  the  plants  under  a  bell  jar  for  more  than  48 
hours  reduced  the  amount  of  infection  obtained  and  appreciably  lengthened 
the  incubation  period.  In  other  experiments  (p.  70)  they  noted  a  tendency 
for  excessively  high  or  excessively  low  humidity  during  the  incubation 
period  to  cause  a  decrease  in  the  size  of  the  urediniospores.  In  another 
experiment  on  soil  moisture  (p.  71)  in  which  three  series  of  plants  were 
employed,  one  of  which  was  heavily  watered,  the  second  moderately,  and 
the  third  received  only  enough  water  to  prevent  the  plants  from  wilting, 
Stakman  and  Levine  found  that  the  plants  in  the  wet  soil  were  more  severely 
attacked  and  that  the  urediniospores  developed  on  them  were  larger  than 
those  in  the  other  two  series.  The  plants  that  suffered  from  drought  pro- 
duced the  smallest  spores.  The  authors  conclude  as  a  result  of  their  study 
on  the  effect  of  environmental  factors  on  the  morphology  of  the  uredinio- 
spore  of  Puccinia  graminis  tritici  that  deficiency  of  soil  moisture  and  of  sun- 
light and  other  ecological  factors  affecting  the  host  plant  unfavorably  ap- 
pear to  be  equally  unfavorable  to  the  rust  parasite. 

Temperature  Relations 

There  is  abundant  evidence  of  a  tendency  towards  physiological  par- 
allelism of  host  and  rust  in  their  temperature  relations. 

Sheldon  (1903,  p.  33)  studied  the  relation  between  greenhouse  tempera- 
ture and  hours  of  sunshine  per  day,  and  the  length  of  the  incubation  period 
in  the  asparagus  rust.  His  experiments  extended  over  a  period  of  five 
months,  from  December,  1900,  to  May,  1901,  and  yielded  data  on  132 
asparagus  plants.  The  results  indicate  an  inverse  relation  between  the 
temperature  and  light  conditions  under  which  the  host  was  growing  and  the 
incubation  period  of  the  rust.  During  December  and  January  the  length 
of  the  incubation  period  was  regularly  14  to  17  days.  During  April  and 
May,  when  the  day  was  longer,  the  light  better,  and  the  temperature 
higher,  the  length  of  the  incubation  period  was  only  8  to  10  days. 


Apr.,  1922]  RAINES  —  VEGETATIVE   VIGOR  OF   THE   HOST  193 

Similar  experiments  with  the  carnation  rust  (Puccinia  Caryophylli  on 
Dianthus  sinensis)  gave  opposite  results.  The  incubation  period  increased, 
from  15  days  in  January  to  21  days  in  May.  In  explanation,  Sheldon 
suggests  the  possibility  that  the  temperature  and  light  in  the  greenhouse 
were  better  suited  to  the  asparagus  than  to  the  pinks.  In  Bailey^s  Cyclopedia 
of  Horticulture  (1914,  p.  670)  the.  carnation  is  characterized  as  a  cool-tem- 
perature plant. 

Several  observers  comment  on  the  lengthening  of  the  incubation  period 
in  cold  weather,  and  the  difficulty  of  obtaining  infection  in  very  warm 
weather.  Christman  (1905,  p.  106)  found  that  in  the  cooler  weather  of 
spring  in  Wisconsin  the  incubation  period  of  cereal  rusts  is  usually  lengthened 
to  between  three  and  four  weeks.  Ward  (1902^,  p.  233)  remarks  that,  in 
working  with  the  brown  rust  of  the  bromes,  he  found  infection  difficult  to 
carry  out  in  hot  weather;  and  in  a  succeeding  paper  (1905,  p.  41)  he  re- 
peats and  emphasizes  the  significance  of  the  observation.  In  this  paper 
(P-  39) »  Ward  also  refers  to  experiments  in  which  the  normal  development 
of  the  rust  was  interfered  with  by  warming  and  chilling  the  root  system  of 
the  host  plant.  Butler  and  Hayman  (1906)  describe  unsuccessful  efforts  to 
produce  artificial  rust  infection  on  plants  growing  in  the  open  in  the  hot 
weather  in  India,  and  express  doubts  whether  the  uredospores  have  power 
to  infect  when  exposed  to  temperatures  exceeding  100°  F.  Fromme  (1913) 
found  that  temperatures  below  20°  C.  increased  the  incubation  period  of 
Puccinia  cor  on  if  era  on  oats. 

Stakman  (1914,  p.  30),  in  his  culture  work  with  cereal  rusts,  observed 
the  incubation  period  to  vary  with  temperature  conditions,  both  high  and 
low  temperatures  lengthening  the  period  very  perceptibly.  Mains  (1917, 
p.  187)  observed  that  low  temperatures  retarded  the  development  of  P. 
coronata  and  P.  Sorghi  in  the  host.  Stakman  and  Levine  (1919,  p.  68) 
report  the  optimum  temperature  for  P.  graminis  tritici  to  be  between  66.5° 
and  70°  F.,  this  giving  the  shortest  incubation  period,  the  most  vigorous 
infection,  and  the  largest  urediniospores,  for  the  host  employed.  At  a 
higher  temperature  than  70°  F.  the  development  of  the  uredinia  was  re- 
tarded at  the  rate  of  one  day  for  every  10  degrees'  rise  in  temperature,  but 
rust  developed  at  as  high  a  temperature  as  the  host  endured  although  the 
size  of  the  urediniospores  produced  was  considerably  decreased.  At  low 
temperatures  the  development  of  the  uredinia  was  retarded  at  the  rate  of 
one  day  for  every  5  degrees'  fall  in  temperature.  Infection  resulted  at  as 
low  temperatures  as  the  host  could  stand.  The  spores  at  the  lower  tem- 
peratures were  rather  small,  but  the  difference  was  not  as  great  as  in  the 
case  of  the  high  temperatures,  with  moderate  temperatures  as  the  basis  for 
comparison. 

Lauritzen  (1919,  p.  19)  reports  experiments  indicating  that  42°  F.  is 
below  the  minimal  temperature  at  which  P.  graminis  tritici  is  able  to  infect 
wheat.  Above  this  temperature  the  amount  of  infection  rises  rapidly  until 


194  AMERICAN   JOURNAL  OF   BOTANY  [Vol.  9, 

at  53°  F.  it  approaches  the  average  for  the  higher  temperatures.  The 
highest  temperature  at  which  the  rust  will  produce  infection  in  wheat  was 
found  to  be  80°  F.  under  the  conditions  of  the  experiments.  The  figures  ob- 
tained by  Johnson  (1912)  are  cited  in  evidence  that  it  is  not  failure  of  the 
spores  to  germinate  which  determines  the  infection  limits  observed  in  the 
experiments.  Johnson  (p.  48)  found  the  optimum  temperatures  for  the 
germination  of  the  uredospores  of  the  common  cereal  grain  rusts  to  be  low 
—12°  to  17°  C. — helping  to  explain  such  observations  as  the  difficulty  of 
keeping  rust  in  culture  in  the  greenhouse  in  the  summer,  when  the  incubation 
period  of  the  rust  is  shorter  than  at  any  other  time  of  the  year  but  it  is  re- 
markably difficult  to  obtain  infection ;  the  difficulty  of  finding  viable  uredo- 
spore  material  in  the  spring,  the  larger  number  of  the  spores  having  already 
germinated;  and  the  favoring  of  rust  development  and  epidemics  by  sub- 
normal temperatures  at  the  critical  infection  periods  in  the  life  of  the  host 
plants. 

Stimulants  and  Depressants ;  Toxic  Agents 

Observations  on  chemical  and  physical  agents  stimulating  or  depressing 
the  vitality  of  the  host  plant  indicate  that  susceptibility  to  rust  infection 
is  affected  in  like  manner. 

Sheldon  (1903,  p.  44)  found  that  in  the  case  of  the  asparagus  rust  and 
the  cai  nation  rust  complete  immunity  to  infection  can  be  produced  by 
lowering  the  vitality  of  the  host — an  end  the  failure  to  achieve  which  in 
the  case  of  the  brown  rust  of  the  bromes  caused  disappointment  to  Ward. 
Concerning  the  asparagus  rust,  Sheldon  states  (p.  44) : 

Attempts  have  been  made  repeatedly  not  only  on  asparagus  but  on  several  species  of 
pinks,  to  inoculate  them  when  they  are  not  growing  well.  It  was  tried  on  repotted  plants, 
those  attacked  by  insects,  and  young  seedlings.  A  failure  was  the  result  in  nearly  every 
case;  while  with  vigorous,  growing  plants  which  had  become  established  there  were  few 
failures — thirty-seven  out  of  forty-two  inoculations  made  at  one  time  being  successful  in 
one  instance — approximately  90  percent. 

In  his  experiments  with  the  carnation  rust  Sheldon  (p.  83)  found  attacks 
by  thrips  a  very  disturbing  factor,  as  it  was  almost  an  impossibility  to 
secure  infection  where  the  thrips  had  worked  to  any  extent  either  before  or 
after  inoculation,  while  vigorously  growing  plants  which  were  free  from 
thrips  were  readily  inoculated. 

Spinks  (1913,  p.  243)  and  Voelcker  (1912,  p.  319)  have  made  observa- 
tions on  the  susceptibility  to  rust  of  the  wheat  plants  grown  in  the  pot- 
culture  experiments  on  the  fertilizing  effects  of  small  quantities  of  the  salts 
of  the  heavy  metals  conducted  at  Woburn,  England.  They  found  that 
the  lithium  salts  of  the  1911  experiments  depressed  susceptibility,  with  the 
exception  of  lithium  nitrate  which  gave  increased  susceptibility  to  rust. 
The  experiments  of  1912  were  with  zinc  salts,  and  they  were  all  found  to 
produce  increased  susceptibility  to  rust,  zinc  nitrate  seeming  particularly 
notable  in  this  respect. 


Apr.,  1922]  RAINES- — VEGETATIVE    VIGOR   OF   THE    HOST  IQ5 

Stakman  (1914,  p.  15)  increased  the  susceptibility  of  cereals  to  rusts 
to  which  they  are  ordinarily  highly  resistant  by  slight  anaesthetization  with 
ether  and  chloroform.  Jost  (1907,  p.  195)  states  that  weak  etherization 
accelerates  respiration,  and  such  treatment  is  usually  considered  as  stimulat- 
ing the  metabolism  of  the  plant.  Stakman  (1914,  p.  39)  also  describes  an 
experiment  in  which  it  was  sought  to  influence  the  susceptibility  of  wheat 
plants  grown  in  water  cultures  by  introducing  various  salts  into  the  culture 
solution.  Copper  sulphate,  copper  carbonate,  and  iron  sulphate  were 
added  in  varying  amounts.  The  results  showed  that  none  of  the  salts  ex- 
perimented with  appreciably  decreased  the  amount  of  rust  when  used  in 
such  concentration  as  to  permit  the  normal  development  of  the  host  plant. 
Infection  was  secured  on  all  the  plants,  even  those  which  were  stunted  to 
one  sixth  their  normal  size. 

Eriksson  and  Hammarlund  (1914)  report  partial  success  in  delaying 
and  inhibiting  the  development  of  Puccinia  malvacearum  on  Althea  rosea 
by  treating  the  soil  with  a  3  to  5  percent  solution  of  copper  sulphate.  They 
give  no  data  on  the  vigor  of  the  plants. 

Bailey  (1920,  p.  76)  found  that  hollyhock  plants  stunted  by  red  spider 
showed  comparative  immunity  to  rust. 

Trauma 

There  are  only  two  recorded  experiments  on  the  effect  of  trauma  on 
susceptibility  to  rust;  they  do  not  agree  in  their  findings.  Trauma  usually 
has  an  immediately  stimulating  effect  on  the  metabolism  of  a  plant  tissue 
and  might  be  expected  to  increase  susceptibility  to  rust.  Hecke  (1915) 
mentions  that  Barfuss  working  in  his  laboratory  has  demonstrated  that 
wheat  rust,  which  ordinarily  does  not  go  to  rye  or  barley,  readily  infects 
rye  and  barley  leaves  if  they  have  previously  been  injured.  After  cultivat- 
ing the  rust  for  seven  generations  on  wounded  leaves,  Barfuss  succeeded  in 
definitely  obtaining  infections  on  uninjured  leaves;  but  these  did  not  mature 
spores.  The  rust  did  not  lose  its  power  to  go  back  to  wheat.  This  is  much 
after  the  manner  of  Salmon's  work  in  increasing  the  susceptibility  of  re- 
sistant host  plants  to  Erysiphaceous  parasites. 

Similar  efforts  to  these  by  Stakman,  also  working  with  cereal  rusts, 
gave  negative  results.  Stakman  (1914,  p.  16)  found  leaf  injury  to  have  no 
effect  on  susceptibility  to  rust. 

In  one  experiment  16  leaves  were  pricked  full  of  holes  in  an  area  of  one  centimeter  or 
more.  They  were  then  inoculated  and  4  became  flecked,  but  no  pustules  developed. 
Histological  examination  showed  that  the  spores  had  sent  out  germ  tubes  in  large  numbers. 
These  grew  among  the  host  cells,  but  true  infection  did  not  take  place.  Sections  of  these 
plants  were  made  and  examined.  It  was  clearly  evident  that  leaf  injury  did  not  increase 
the  chances  for  infection. 


196  AMERICAN   JOURNAL   OF    BOTANY  '[Vol  9. 

Age  and  Maturity  of  Host  Tissue 

In  his  experiments  with  the  asparagus  rust  Sheldon  (1903,  p.  47)  found 
a  great  difference  in  susceptibility  in  favor  of  young  and  vigorously  growing 
shoots  as  against  older  shoots  of  the  same  plant.  His  observations  indicated 
that 

The  incubation  period  of  the  rust  on  plants  of  the  same  age  and  growing  in  the  same 
pot  so  that  conditions  were  practically  identical,  was  very  uniform.  When  the  plants  were 
of  the  same  age  and  growing  in  the  same  kind  of  soil  in  different  pots,  there  was  still  a  uni- 
formity. But  when  there  was  a  difference  in  maturity,  as  of  two  shoots  from  the  same 
root,  or  several  plants  growing  in  the  same  pot,  there  was  a  difference  in  the  time — of  four 
days  in  one  instance,  the  young  growing  shoots  showing  sori  first.  The  sori  showed  first 
on  the  young  growing  shoots,  and  developed  faster  and  to  larger  size.  The  more  robust 
the  shoot,  the  larger  the  sori  were  and  the  more  spores  they  produced. 

Sheldon  found  practically  no  difference  between  young  shoots  of  young 
and  old  plants.  A  few  shoots  from  three-year-old  plants  growing  in  the 
same  pots  showed  rust  the  same  day  that  the  seedlings  did.  Sheldon  made 
similar  observations  on  the  carnation  rust. 

An  age  factor  of  a  different  kind  is  reported  by  Sheldon  (1905,  p.  227) 
in  the  susceptibility  of  onions  to  Puccinia  Asparagi.  Complete  immunity 
was  found  when  seedling  onions  were  inoculated  with  the  rust.  The  inocu- 
lations were  begun  as  soon  as  the  seedlings  appeared  above  ground,  and 
were  repeated  at  intervals  until  the  seedlings  were  two  months  old,  when 
almost  every  inoculation  was  successful. 

Galloway  (1903,  p.  208)  reports  a  maturity  factor  as  seemingly  affecting 
the  susceptibility  of  wheat  to  rust.  In  his  extensive  experiments  on  the 
possibility  of  controlling  cereal  rusts  by  means  of  spraying  or  soil  treatment, 
Galloway  found  that  the  rust,  while  abundant  on  the  primary  experimental 
plots,  was  absent  from  nearly  all  the  duplicate  plots.  The  latter  had  been 
planted  a  week  to  ten  days  later  than  the  oiiginal  plots,  and  in  point  of 
growth  were  at  least  as  much  behind  them  at  the  time  of  observation.  As 
the  experiments  were  with  a  winter  wheat,  planted  the  preceding  fall,  it 
cannot  have  been  that  the  plants  of  the  duplicate  plots  had  missed  a  wave 
of  inoculating  material. 

Miss  Gibson  (1904,  p.  188)  reports  the  presence  of  a  seasonal  factor  in 
the  susceptibility  of  certain  varieties  of  chrysanthemum  to  the  chrysan- 
themum rust.  She  noticed  that  certain  varieties  do  not  take  the  rust  in 
summer,  although  growing  in  the  midst  of  plants  thickly  covered  with  it. 
As  the  rust  spores  germinate  well  in  summer  and  the  germ  tubes  penetrate 
readily,  it  is  a  problem  not  in  the  physiology  of  the  parasite  but  rather  in 
that  of  the  host. 

Stakman  and  Piemeisel  (1917,  p.  486),  in  their  extensive  inoculation 
work  with  cereal  and  grass  rusts,  found  the  cereals  and  Dactylis  glomerata 
apparently  equally  susceptible  at  all  ages  up  to  ripening  time.  Agropyron 
and  Elymus  were  extremely  susceptible  when  young  and  much  less  so  when 


Apr.,   1922]  RAINES VEGETATIVE    VIGOR   OF   THE   HOST  197 

older.  On  the  other  hand,  Phletim  pratense  and  Agrostis  alba  were  more 
susceptible  when  older. 

Stakman  and  Levine  (1919,  p.  73)  observed  an  age  difference  in  the 
progress  of  an  infection  of  P.  graminis  avenae  on  oats.  Plants  that  were 
one  week  old  at  the  time  of  inoculation  were  somewhat  more  heavily  in- 
fected at  first  than  plants  one,  two,  and  four  weeks  older;  but  at  the  end  of 
ten  days  the  infection  was  heavier  on  the  older  plants,  especially  so  on  the 
plants  that  were  three  weeks  old  at  the  time  of  inoculation.  The  size  of 
the  urediniospores  was  uniform  regardless  of  the  age  of  the  host,  nor  was 
any  difference  observed  in  the  shape  and  color  of  the  spores.  They  also 
state  that 

.  .  .  the  junior  author  has  obtained  very  successful  infection  on  mature  plants  of  more 
than  a  hundred  different  varieties  of  wheat,  grown  in  the  greenhouse  and  artificially  inocu- 
lated with  P.  graminis  tritici. 

Giddings  (1918,  p.  33)  found  susceptibility  in  apple  leaves  to  infection  by 
Gymno sporangium  juniperi-mrginiana  to  be  limited  to  young  leaves,  not 
more  than  fifteen  to  twenty- four  days  old  after  unrolling  from  the  bud, 
older  leaves  being  almost  completely  resistant.  H.  H.  York  (personal 
communication)  has  found  that  the  very  young  leaves  of  Ribes  are  resistant 
to  infection  by  Cronartium  ribicola,  susceptibility  not  appearing  until  some 
time  after  the  unfolding  of  the  leaf. 

The  factor  of  age  and  maturity  of  host  tissue  is  reviewed  here  briefly 
because  of  its  close  association  in  thought  with  vegetative  vigor.  There  is 
no  necessary  physiological  connection  between  the  two  factors,  and  their 
significance  in  susceptibility  and  resistance  to  rust  infection  is  probably  of 
a  different  nature.  The  age  factor  in  disease  resistance  is  probably  to  be 
classed  rather  with  varietal  and  constitutional  differences  than  with  physi- 
ological condition. 

FIELD  STUDIES  AND  EXPERIMENTS 

A  series  of  studies  was  made  to  determine  the  general  facts  as  to  the 
occurrence  and  epidemiology  of  the  rusts  on  the  cereal  grains  in  the  so  called 
local-flora  region  of  New  York,  and  especially  for  the  New  York  Botanical 
Garden  and  vicinity.  Data  as  to  the  points  involved  were  found  to  be 
very  meager,  and  these  preliminary  studies  were  made  as  a  contribution  to 
the  general  problem  of  rust  epidemiology  in  the  Atlantic  States,  a  field  so 
far  little  studied  because  of  the  relative  unimportance  of  grain  growing  in 
these  regions.  More  especially  also  it  was  desired  to  lay  a  foundation  for 
future  studies  of  rust  problems  which  presuppose  a  knowledge  of  the  general 
behavior  of  the  rusts  under  the  climatic  and  other  conditions  of  the  region. 

The  Rusts  of  the  Cereal  Grains  and  Related  Grasses 
in  the  Vicinity  of  New  York 

The  time  of  first  appearance,  period  of  greatest  virulence,  and  even  the 
identity  of  the  rusts  on  the  cereal  grains  and  related  grasses  which  have  been 


198  AMERICAN   JOURNAL   OF    BOTANY  [Vol.  9, 

suspected  of  harboring  cereal  rusts  in  the  vicinity  of  New  York  City  cannot 
be  regarded  as  accurately  determined. 

The  herbarium  of  the  New  York  Botanical  Garden  contains  17  col- 
lections of  four  different  species  of  rusts  on  cereal  grains  and  grasses  which 
might  bear  related  rusts  from  the  region  about  New  York  City,  the  so  called 
local-flora  region,  as  follows: 

Puccinia  rubigo-vera  DC.  (Puccinia  dispersa  Eriks.  &  Henn.  ex  parte): 
On  wheat,  at  Cedarville,  N.  J.,  June  3,  1880.     Ellis  collection  (II). 
On  rye,  at  Flatbush,  L.  I.,  May  25,  1889,  by  Zabriskie  (II). 
Puccinia  poculiformis  (Jacq.)  Kuntz  (Puccinia  graminis  Pers.): 

On  wheat,  at  Greencastle,  Putnam  Co.,  N.  Y.,  September,  1893,  by  L.  M.  Underwood 

(II,  HI). 
On  oats,  at  Greencastle,  Putnam  Co.,  N.  Y.,  September,  1893,  by  L.  M.  Underwood 

(II,  HI). 
On  oats,  at  the  New  York  Botanical  Garden,  October,  1900,  by  the  class  in  mycology 

(II,  HI). 

On  Anthoxanthum  odoratum,  at  Newfield,  N.  J.,  May  4,  1890.     Ellis  collection  (III). 
On  Ammophila  brevipile  Torr.,  at  Egg  Harbor,  N.  J.,  188-,  by  S.  M.  Tracy  (III). 
On  Agrostis  vulgaris  L.,  at  Plainville,  Conn.,  August  23,   1883,  by  A.   B.  Seymour 

(II,  HI). 
On  Poa  pratensis  L.,  at  Greencastle,  Putnam  Co.,  N.  Y.,  September,  1893,  by  L.  M. 

Underwood  (III). 

On  Berberis  vulgaris  L.,  at  Newfield,  N.  J.,  May  24,  1875.     Ellis  collection  (I). 
On  J).  vulgaris,  at  Newfield,  N.  J.,  May,  1881.     Ellis  collection  (I). 
On  B.  vulgaris,  at  Richmond  Hill,  L.  I.,  May  22,  1889,  by  S.  E.  Jelliffe  (I). 
Puccinia  andropogonis  Schw. : 

On  Aureolaria  villosa  (Muhl.)  Raf.  (Gerardia  villosa  Muhl.),  at  Newfield,  N.  J.,  June, 

1874,  by  Gerard  (I). 

On  Gerardia  quercifolia  Pursh.,  at  Westville,  Conn.,  June,  1890,  by  R.  Thaxter  (I). 
Puccinia  Ellisiana  Thum.: 

On  Andropogon  sp.,  at  Newfield,  N.  J.,  September,  1897.     Ellis  collection  (III). 

On  Andropogon  Scoparius  Michx.,  at  New  Haven,  Conn.,  October  4,  1913,  by  J.  M. 

Bates  (III). 
On  Viola  pedata  L.,  at  New  Haven,  Conn.,  May  31,  1841,  by  Manlius  Smith  (I). 

I  have  also  found  the  following  notes  on  the  occurrence  of  these  forms 
in  the  local-flora  region.  Peck  (1871,  p.  121),  in  his  list  of  the  Pucciniae  of 
New  York  State,  lists  P.  coronata  Cord,  as  common  on  the  leaves  of  grasses 
and  cereals  in  August  and  September,  and  P.  graminis  Pers.  as  common  on 
the  leaves  and  sheaths  of  grasses  and  cereals  in  autumn  and  spring.  Thaxter 
(1890,  p.  98)  notes  the  abundant  occurrence  of  P.  rubigo-vera  DC.  (probably 
P.  dispersa  Eriks.  and  Henn.)  on  rye  in  Connecticut  in  the  year  1890, 
describing  it  as  covering  the  leaves  with  its  rust-covered  uredo  form  and 
doing  considerable  damage. 

Humphrey  (1891,  p.  228)  remarks  on  the  occurrence  of  rust  (Puccinia 
sp.)  on  rye  in  Massachusetts  in  1891.  He  records  some  interesting  obser- 
vations on  the  mode  of  wintering  over  of  the  fungus.  The  rust,  he  notes, 
appeared  on  rye  in  June  so  abundantly  that  the  spores  rose  in  clouds  when 
the  plants  were  touched.  In  July  this  stage  of  the  fungus  had  largely 


Apr.,  1922]  RAINES  —  VEGETATIVE    VIGOR   OF   THE   HOST 

disappeared,  and  the  winter  pustules  were  mainly  in  evidence.  Observa- 
tions seemed  to  indicate  that  the  rust  does  not  survive  the  winter  in  its 
host  plant  but  depends  upon  fresh  infection  in  the  spring  on  the  plots  of  the 
Massachusetts  Agricultural  Experiment  Station.  In  this  connection  Hum- 
phrey notes  that  uredosori  on  rye  seedlings  survived  the  early  frosts  and 
seemed  vigorous  until  the  heavy  frosts  and  snowfalls.  The  plots  were  then 
covered  with  snow  until  spring.  When  they  were  again  exposed,  the  dis- 
colored spots  where  the  pustules  had  been  could  be  readily  observed,  and 
examination  showed  mycelium  to  be  present  in  the  spots;  but  it  was  appar- 
ently dead,  for  repeated  examination  of  the  plot  failed  to  detect  new  spores 
breaking  out  from  any  of  the  old  spots.  The  fungus  was  not  observed  after 
growth  was  resumed  until  early  in  June. 

Jelliffe  (1889,  p.  35)  reports  Puccinia  graminis  Pers.  on  the  barberry 
and  on  wheat  as  of  frequent  occurrence  throughout  Long  Island.  Clinton 
(1903)  reports  the  occurrence  in  Connecticut  of  P.  rubigo-vera  DC.  (probably 
P.  dispersa  Eriks.  &  Henn.)  on  rye  and  barley,  of  P.  graminis  Pers.  on  rye, 
barley,  oats,  red-top,  and  timothy,  and  of  P.  coronata  Cord,  on  the  leaves  of 
Rhamnus  cathartica,  Notoholcus  lanatus,  and  Avena  saliva.  The  outbreaks 
of  the  last,  Clinton  notes,  are  not  nearly  so  prolonged  or  prominent  as  those 
of  P.  graminis.  Burnham  and  Latham  (1914)  report  finding  P.  coronata 
Cord,  on  the  leaves  of  Rhamnus  cathartica,  Notoholcus  lanatus,  and  Avena 
sativa  at  Sothold,  L.  I.  They  also  report  the  occurrence  there  of  P. 
graminis  Pers.  on  Berberis  vulgaris  and  on  the  leaves  of  various  grasses,  and 
of  P.  triticina  Eriks.  on  various  species  of  Triticum. 

During  the  summer  and  fall  of  1916  the  writer  collected  the  following 
cereal  and  grass  rusts  in  the  so  called  "local-flora  region,"  i.e.,  the  region 
within  one  hundred  miles  of  New  York. 

Puccinia  dispersa  Eriks.  &  Henn.: 

On  wheat,  five  collections:  at  Lakehurst,  N.  J.,  June  6  (II)  and  August  23  (II,  III); 
at  Yonkers,  N.  Y.,  July  16  (II);  at  New  Brunswick,  N.  J.,  July  24  (II);  at  Williams- 
bridge,  N.  Y.,  July  19  to  September  (II,  III);  at  the  New  York  Botanical  Garden, 
July  17  to  October  (II,  III). 

On  rye,  eight  collections:  at  Tom's  River,  N.  J.,  June  3  (II,  III);  at  Lakehurst,  N.  J., 
June  20  (II,  III);  at  Yonkers,  N.  Y.,  July  16  (II);  at  Queens,  L.  I.,  June  15  (II); 
at  New  Brunswick,  N.  J.,  July  24  (II);  at  Williamsbridge,  N.  Y.,  July  19  (II); 
at  the  New  York  Botanical  Garden,  July  17  to  October;  at  Nyack,  N.  Y.,  July  8 
(II). 

On  barley,  two  collections:  at  Williamsbridge,  N.  Y.,  September  13  (II);  at  the  New 
York  Botanical  Garden,  September  15  (II). 

On  Agropyron  repens,  three  collections:  at  Tom's  River,  N.  J.,  July  4  (II);  at  Williams- 
bridge,  N.  Y.,  July  19  (II);  at  the  New  York  Botanical  Garden,  July  8  to  October 
(II,  HI). 

These  rusts  correspond  closely  with  Eriksson  and  Henning's  Puccinia 
dispersa  (Puccinia  rubigo-vera  DC.  pro  parte).  The  uredo  of  the  above- 
listed  collections  is  amphigenous.  The  number  of  pustules  on  the  upper 
surface  is  somewhat  in  excess  of  that  on  the  lower  surface,  counts  on  pieces 


2OO  AMERICAN   JOURNAL  OF   BOTANY  [Vol.  9. 

of  leaf  I  cm.  in  length  giving  the  numbers  174  to  158,  and  217  to  195  re- 
spectively.    The  sori  on  the  upper  surface  are  more  pulverulent. 

The  uredos  on  the  wheat,  rye,  and  Agropyron  were  certainly  not  dis- 
tinguishable by  morphological  characters.  The  pustules  on  the  barley 
show  very  little  pulverulence.  Measurements  of  the  pustules  on  the  barley 
(measurements  being  made  on  the  size  of  the  rupture  in  the  epidermis) 
show  them  to  be  of  the  same  size  as  the  pustules  on  the  other  hosts  of  P. 
disperse, .  The  spores  of  the  barley  rust  are  narrower  than  those  on  the 
other  cereals.  Twenty-five  spores  gave  an  average  ratio  of  length  to  width 
of  1. 218.  Seven  such  measurements  on  wheat  gave  ratios  ranging  from 
1.083  to  1.163. 

Puccinia  graminis  Pers. : 

On  Phleum  pratense,  at  Tom's  River,  N.  J.,  August  23.  Only  II  was  found  on  this 
host,  as  others  have  noted. 

On  oats,  at  Tom's  River,  N.  J.,  August  23  (II,  III);  at  Williamsbridge,  N.  Y.,  August 
16  (II,  III);  at  the  New  York  Botanical  Garden,  August  26  (II,  III).  The  rust 
was  never  abundant,  occurring  as  a  thin  sprinkling  on  the  leaves  and  sheaths 
among  the  crown-rust  sori,  and  on  the  culms.  The  long,  rectangular,  erumpent 
teleutosori  are  very  conspicuous  scattered  among  the  mass  of  smaller,  covered  sori 
of  the  crown  rust. 
Puccinia  coronifera  Kleb. : 

On  oats,  at  Williamsbridge,  N.  Y.,  August  2  to  September  (II,  III);  at  the  New  York 
Botanical  Garden,  August  12  to  October  (II,  III);  at  Tom's  River,  N.  J.,  August  23 
(II,  HI)- 

The  crown  rust  of  the  present  collections  differs  in  some  minor  particulars 
from  the  published  descriptions  I  found  it  somewhat  later  in  its  appear- 
ance on  the  sheath,  but  both  uredo  and  teleuto  in  the  end  are  as  abundant 
on  the  sheath  as  on  the  leaf  blade.  Eriksson  and  Henning  (p.  240)  found  it 
"  rarely  on  the  sheath."  Both  the  uredo  and  the  teleuto  occur  in  abundance 
on  the  lower  and  the  upper  surfaces  of  the  leaves,  but  the  uredo  is  always 
in  excess  on  the  upper  surface  while  the  teleuto  first  appears  and  is  always 
in  advance  in  its  development  on  the  under  surface.  Grove  (p.  256)  and 
Fischer  (p.  375)  describe  the  teleuto  as  hypophyllous.  The  most  con- 
siderable discrepancy  between  the  descriptions  of  Grove  and  Plowright  and 
the  rust  here  described  is  in  the  number  of  the  germ  pores.  Five  spores  of 
which  the  germ  pores  were  counted  showed  respectively  9,  9,  9,  n,  and  8 
pores.  The  germ  pores  as  well  as  the  spines  are  inconspicuous  until  brought 
out  by  treatment  with  lactic  acid.  Grove  (p.  256)  and  Plowright  (p.  164) 
describe  the  germ  pores  as  3  to  4  in  number.  Fischer  (p.  275)  simply  icfers 
to  them  as  inconspicuous,  and  Eriksson  and  Henning  (p.  240)  do  not  men- 
tion them  in  their  description  of  the  crown  rust. 

Puccinia  impatientis  (Schw.)  Arth.: 

On  Elymus  virginicus  L.,  at  Valley  Stream,  L.  I.,  August  12  (II);  at  Hackensack,  N.  J., 
September  18  (III);  at  the  New  York  Botanical  Garden,  June  to  October  (II,  III). 

At  the  last-named  station  Impatiens  aurea  Muhl.  near  by  was  infected 


Apr.,  1922]  RAINES —  VEGETATIVE   VIGOR  OF    THE   HOST  2OI 

with  an  aecidium.  The  uredospores  of  this  form  are  markedly  less  rounded 
and  the  teleutosori  are  much  longer  than  in  the  case  of  the  wheat  and  rye 
rusts  as  I  have  found  them.  The  rust  on  Elymus  has,  however,  been  classed 
with  P.  rubigo-vera  DC. 

Puccinia  poculiformis: 

On  Cinna  arundinacea,  at  Jerome  Avenue,  New  York  City,  September  15  (III). 

An  Experiment  to  Determine  the  Time  and  Method  of  First  Appearance  of 

the  Rust,  in  which  the  Source  and  Condition  of  the  Seed 

as  Possible  Factors  are  also  Tested 

In  investigations  of  a  physiological  nature  on  the  cereal  rusts  it  is  de- 
sirable that  the  probability  be  established  that,  for  the  variables  being 
compared,  the  source  of  the  fungus  being  worked  with  is  constant.  This 
point  in  experimental  method  assumes  particular  importance,  in  investiga- 
tions such  as  are  the  subject  of  the  present  paper,  from  the  recent  demon- 
stration of  the  variation  in  physiological  properties  of  strains  of  rust  from 
different  localities.  Assuming  that  the  rust  endemic  in  any  locality  is 
fairly  constant  in  its  behavior  (whether  the  constancy  is  due  to  actual 
genetic  purity,  or  to  an  admixture  of  strains  in  constant  proportions),  a 
possible  source  of  error  would  be  the  seed  transmission  of  the  rust,  making 
the  source  and  condition  of  the  seed  a  factor  in  determining  the  nature  of 
the  rust.  Critical  evidence  on  the  question  of  the  role  played  by  the  seed 
in  the  first  appearance  of  rust  on  cereals  in  early  summer  is  still  lacking. 
As  against  the  feeling  of  necessity,  almost,  in  the  minds  of  some  investi- 
gators, of  the  assumption  of  seed  transmission  of  the  rusts  in  explaining 
certain  phenomena  in  the  epidemiology  of  these  diseases,  must  be  counted 
the  inability  to  demonstrate  with  certainty  a  means  of  transmission,  or  to 
observe  seed  transmission  of  cereal  rusts  under  controlled  experimental 
conditions. 

To  test  the  possible  role  played  by  the  seed  in  determining  the  first 
appearance  of  rust  under  field  conditions  in  the  vicinity  of  New  York,  25 
patches  of  wheat,  8  patches  of  barley,  one  patch  of  rye,  and  one  patch  of 
oats  were  planted  with  seed  from  widely  different  sources,  and  of  varying 
age  and  condition  on  a  plot  of  ground  near  the  New  York  Botanical  Garden. 
The  plantings  were  made  on  high,  well  drained  land  which  had  not  been 
cultivated  since  1912,  when  it  had  been  put  to  corn.  The  nearest  plot  of 
cereal  was  a  field  of  oats  about  one  quarter  mile  away,  and  there  were  no 
other  grain  fields  within  a  distance  of  one  mile  at  least.  It  is  not  thought 
that  this  single  experiment  is  of  very  great  significance  as  to  the  general 
question  of  possible  seed  transmission  of  rust.  It  is  of  interest,  however, 
to  include  such  inferior  seed  as  that  planted  in  the  first  three  plots  in  a  test 
as  to  the  time  of  appearance  of  the  rust. 

The  varieties  planted,  the  source  of  the  seed,  and  the  date  the  rust  first 
appeared  on  the  plants  are  shown  in  table  2. 


; 


202 


AMERICAN   JOURNAL  OF   BOTANY 


[Vol.  9, 


TABLE  2 
(The  designations  "screening  wheat,"  "smutted  wheat,"  etc.,  are  the  millers'  terms) 


Plot 
No. 

Cereal 
Planted 

Variety 

Source  of  Seed 

Date  Rust  First 
Appeared 

I  

Wheat 

"Rusted  wheat" 

Fargo   Milling   Co.,    Fargo,    N.    D., 

1915 

July  19 

2  

11 

"Smutted  wheat" 

Washburn-Crosby  Co.,  Minneapolis, 

Minn.,  1915 

t  I 

3.... 

ii 

"Screening  wheat" 

Fargo    Milling   Co.,   Fargo,    N.    D., 

I9I5 

4.... 

ii 

Haynes  Bluestem 

Arlington  Station,  1912 

5.... 

" 

Minnesota  no.  163 

Akron  Substation,  1912 

6.... 

« 

no.  163 

Arlington,  1912 

7.... 

n 

no.  188 

Minn.  Exp.  Station,  1912 

8.... 

« 

no.  181 

Minn.  Exp.  Station,  1912 

9.... 

« 

no.  169 

Minn.  Exp.  Station,  1912 

10  

" 

Rural  New  Yorker 

Arlington  Station,  1912 

ii  

4< 

Early  Genesee  Giant 

Akron  Substation,  1912 

12  

11 

Dawson's  Golden 

Chaff 

Arlington  Station,  1912 

13.... 

ii 

Early  Red  Chief 

Arlington  Station,  1912 

14.... 

" 

Seneca  Chief 

Wis.  Exp.  Station,  1912 

IS---- 

11 

Fish-head 

Minn.  Exp.  Station,  1912 

16.... 

11 

Red  Russian 

Akron  Substation,  1912 

17  

" 

Amantka 

Akron  Substation,  1912 

18.... 

" 

Galgalos 

Akron  Substation,  1914 

19.... 

i 

Little  Club 

Arlington  Station,  1913 

20  

< 

Wasnani 

Akron  Substation,  1913 

21  

< 

Erivan 

Akron  Substation,  1913 

22  

< 

Ghanooka 

Wis.  Exp.  Station,  1912 

23  

1 

Beloturka 

Akron  Substation,  1912 

24.... 

' 

Macaroni 

Wis.  Exp.  Station,  1914 

25  

1 

Rupert's  Giant 

Thorburn  Co.,  1916 

26  

Rye 

Spring 

Thorburn  Co.,  1916 

27.... 

Oats 

Tartar  King 

Thorburn  Co.,  1916 

August  2 

28.... 

Barley 

White  Smyrna 

Akron  Substation,  1912 

Sept    13 

29.... 

« 

Chevalier 

Minn.  Exp.  Station,  1912 

30.  ... 

ii 

Black  Hulless 

Hays  Exp.  Station,  1913 

SI.-- 

a 

White  Hulless 

Hays  Exp.  Station,  1913 

32.... 

11 

Swankali 

Minn.  Exp.  Station,  1912 

33---- 

" 

Telli 

Arlington  Station,  1912 

34.... 

a 

Gaitami 

Arlington  Station,  1912 

35--.- 

ii 

Wis.  Fed.  no.  5 

Minn.  Exp.  Station,  1913 

As  the  table  shows,  the  rust  appeared  simultaneously  on  all  the  plots  of 
wheat  and  barley  respectively.  It  appeared  at  the  same  time  on  a  resistant 
variety  such  as  the  Macaroni  wheat  and  on  a  susceptible  variety  such  as 
Rupert's  Giant;  on  plants  grown  from  seed  coming  from  North  Dakota 
and  on  plants  grown  from  seed  coming  from  Maryland;  on  plants  from 
good,  plump  seed  and  on  plants  grown  from  seed  rejected  by  the  miller, 
such  as  the  "rusted  wheat"  and  the  "screening  wheat"  seed.  Evidently 
the  nature  and  first  appearance  of  the  rust  were  determined  by  local  environ- 
mental conditions,  and  variety,  age,  source,  and  condition  of  the  seed  played 
a  subordinate  role  at  least  in  this  particular  case.  It  is  also  to  be  noted 
that  the  rust  appeared  at  different  times  on  the  different  cereals  except  in 


Apr.,  1922!  RAINES VEGETATIVE    VIGOR   OF   THE    HOST  2O3 

the  case  of  wheat  and  rye.  This  may  be  regarded  as  further  evidence,  if 
any  be  required,  of  the  physiological  distinction  of  the  rubigo-vera  forms 
growing  on  wheat  and  rye  on  the  one  hand,  and  on  barley  and  oats  on 
the  other. 

Hungerford  (1920,  p.  270)  reports  an  experiment  testing  the  time  of 
first  appearance  of  rust  on  wheat  plants  grown  from  rust-infected  and  from 
clean  seed,  similarly  indicating  that  the  condition  of  the  seed  does  not 
affect  the  time  of  first  appearance  of  the  rust. 


VEGETATIVE  VIGOR  OF  THE  HOST  AS  A  FACTOR  INFLUENCING 

SUSCEPTIBILITY   AND   RESISTANCE   TO  CERTAIN 

RUST   DISEASES   OF   THE   HIGHER   PLANTS 

II 

M.  A.  RAINES 
(Received  for  publication  July  13,  1921) 

FURTHER  FIELD  STUDIES  AND  EXPERIMENTS 

The  Rust  History  of  Plots  of  Cereals  Sown  at  Successive  Intervals 
through  the  Summer 

To  test  the  susceptibility  to  rust  of  plants  of  different  ages  at  each  period 
of  the  summer  and  of  young  plants  at  different  times  in  the  summer,  and 
1o  follow  the  subsequent  history  of  the  disease  on  plantings  of  cereals 
started  at  successive  intervals  through  the  season,  plots  of  wheat,  rye, 
oats,  and  barley  were  started  in  the  breeding  plot  of  the  New  York  Botanical 
Garden  on  June  10,  June  23,  July  6,  July  20,  August  5,  and  August  25,  1916. 
Observations  were  made  at  intervals  on  the  height  of  the  plants,  the  time  of 
first  appearance  of  the  rust,  the  amount  of  infection,  and  the  proportion 
of  the  rust  in  the  teleuto  stage. 

The  results  for  the  different  cereals  are  shown  in  table  3  and  are  discussed 
below.  In  the  table,  the  days  on  which  the  observations  were  made  are 
£:iven  at  the  top.  The  height  of  the  plants  is  given  in  inches  (").  When 
the  plants  have  headed,  it  is  indicated  by  an  "H."  The  degree  of  rust 
infection  is  indicated  by  a  numeral,  and  was  estimated  on  a  scale  of  10, 
ihe  values  of  the  numbers  in  the  scale  being:  i  =  an  occasional  pustule 
here  and  there;  most  of  the  leaves  not  affected.  2  =  most  of  the  leaves 
with  from  one  to  five  sori.  3  =  about  ten  pustules  on  each  leaf.  4  = 
leaves  heavily  infected.  5  =  leaves  bearing  the  maximum  possible  amount 
of  rust.  6  =  leaf  sheaths  infected  as  well  as  the  leaf  blades.  7  =  a 
sprinkling  of  rust  sori  on  the  stem  and  leaf  sheaths;  blades  heavily  infected. 
<S  =  infection  on  sheath  and  stem  well  developed.  9  =  heavy  infection 
on  the  stem.  10  =  heaviest  possible  infection  on  the  whole  plant.  The 
leleuto  stage  is  indicated  by  its  Roman  numeral,  "III."  A  fraction  pre- 
ceding the  "III "  gives  the  proportion  of  the  rust  in  the  teleuto  form. 

As  is  indicated  in  table  3,  the  plots  of  wheat  planted  on  June  10  and 
June  23  headed  out  in  77  and  64  days  respectively.  Those  planted  July  6, 
July  20,  August  5,  and  August  25  never  headed  and  never  exceeded  a 
height  of  20  inches.  The  rust  invariably  appeared  on  the  young  plot  as  a 
thin,  evenly  distributed  infection  when  the  host  plant  was  putting  out  its 

215 


216 


AMERICAN   JOURNAL   OF   BOTANY 


[Vol.  9 


TABLE  3 
Wheat 


Observations 

Date 
Sown 

JulyS 

July  17 

July  24 

Aug.  12 

Aug.  26 

Sept.  15 

Oct.  i 

Oct.  23 

No.  of  Days 
to  Head 

June  10.  .  . 

8"-2 

I2"-4 

l8"-4 

24"~5 

H-6 

7 

7 

77 

slight 

III 

June  23... 

2" 

9"-2 

I2"-4 

2O"~4 

H-5 

6 

7 

6 

64 

slight 

slight 

slight 

July  6.... 
July  20.  .. 

5" 

8"-l 

i5;;-5 

io"-3 

i8"-5 
i2"-5 

i8"-5 
i5"-4 

20"-5 

2o"-5 

20"-4 
20"-3 

Aug.  5-... 

9"-3 

10-4 

i5"-5 

15-4 

Aug.  25... 

5"~2 

9-4 

i5"-3 

Rye 


Observations 

Date 

jNo.  ot  Days 

Sown 

JulyS 

July  17 

July  24 

Aug.  12  1  Aug.  26 

Sept.  15 

Oct.  i 

Oct.  23 

to  Head 

j 

June  10.  .  . 

de- 

stroyed 

June  23... 
July  6.... 
July  20.  .  . 

3" 

r 

20"-2 

8"-i 

H-3 

'i-:? 

3-5 

I2"-4 

6 
i8"-6 

7 
H-7 

7  • 
I 

33 
51 
73 

Aug.  5---- 

4"-i 

io"-5 

i5"-6 

H-5 

79 

Aug.  25... 

8"-2 

io"-5 

20-4 

Oats 


Date 
Sown 

Observations 

No.  of  Days 
to  Head 

JulyS 

July  17 

July  24 

Aug.  12 

Aug.  26 

Sept.  15 

Oct.  i 

Oct.  23 

June  10.  .  . 

10" 

I4" 

18" 

H-2 

6 

8 

9 

77 

slight 
III 

slight 
III 

KHI 

all  III 

June  23... 

5" 

10" 

18" 

24"-2 

slight 

H-7 
1AUI 

8 
Kill 

alHII 

Q 

all  III 

63 

III 

July  6.... 

4" 

8" 

I5"-2 

slight 
III 

20"~6 

slight 
III 

H-8 
%lll 

8 
KHI 

o 

all  III 

70 

July  20.  .. 

IO"-I 

1  2  "-3 

slight 

i8"-5 
^III 

24"-6 

Mill 

H-8 
K  HI 

91 

III 

Aug.  5.... 

9"-i 

i5"-5 
slight 

i8"-5 
^IH 

20"-7 

Kin 

III 

Aug.  25... 

6"-i 

IO"-2 

3ti 

May,  1922] 


RAINES  —  VEGETATIVE    VIGOR   OF   THE    HOST 
Barley 


217 


Observations 

Date 
Sown 

July  8 

July  17 

July  24 

Aug.  12 

Aug.  26 

Sept.  15 

Oct.  i 

Oct.  23 

No.  of  Days 
to  Head 

June  10.  .  . 

8" 

15" 

H 

2 

I 

44 

June  23.  .  . 

4" 

15"     !     18" 

H 

I 

3 

50 

July  6.  .  .  . 

3" 

8" 

15" 

H 

i 

I 

50 

July  20.  .. 

9" 

15" 

20" 

H 

70 

Aug.  5.... 

6" 

10" 

15" 

15" 

Aug.  25... 

6" 

10" 

12" 

third  leaf.  The  rust  increased  steadily  in  abundance  on  the  leaf  blade 
until  it  reached  the  maximum,  and  only  then  began  to  appear  on  the  leaf 
sheaths.  On  the  stem  there  were  never  more  than  a  few  scattered  pustules. 
Teleutosori  did  not  appear  until  the  middle  of  September.  They  were  to 
be  found  only  on  plants  of  the  two  oldest  plots,  and  then  not  without  care- 
ful search.  The  observations  of  October  23  showed  a  distinct  drop  in  the 
amount  of  rust  on  all  the  plots  of  wheat.  The  new  leaf  growth  of  October 
tended  to  show  but  little  rust.  In  view  of  Johnson's  (1912)  findings  that 
low  temperatures  promote  uredospore  germination,  these  observations 
may  be  interpreted  as  indicating  greater  resistance  to  rust  infection  on  the 
part  of  the  host  tissue  due  to  the  decreased  rate  of  metabolic  activity  con- 
sequent on  the  onset  of  cooler  weather. 

All  of  the  plots  of  rye  except  that  sown  August  25  headed  out,  but  the 
rate  of  growth  varied  as  is  indicated  by  the  successively  greater  intervals 
required  by  the  younger  stands  to  head  out.  The  behavior  of  the  rust  on 
the  plots  of  rye  was  much  the  same  as  on  the  wheat.  In  the  younger 
plantings  it  was  somewhat  less  marked  and  less  severe  than  on  the  wheat 
plants  of  the  same  age,  but  the  development  of  the  rust  was  more  severe 
on  the  rye  than  on  the  wheat.  It  seemed,  too,  to  go  more  readily  to  the 
leaf  sheaths  and  stems  in  the  case  of  the  rye.  No  teleuto  was  found  on 
the  rye. 

Of  the  oats,  the  first  three  plots  headed  out  in  77,  65,  and  70  days 
respectively;  the  fourth  plot  produced  only  one  head,  91  days  after  planting. 
The  plots  planted  August  5  and  August  25  never  headed  out.  No  rust 
appeared  on  the  oats  until  August  12  when  four  plots  were  up,  ranging  in 
age  from  seedlings  in  the  four-leaf  stage  to  plants  in  bloom.  The  rust 
appeared  on  all  four  of  the  plots  at  the  same  time  and  in  relatively  the 
same  abundance.  However,  once  the  rust  had  appeared,  its  subsequent 
history  on  the  various  plots  differed  decidedly.  The  older  the  plant,  the 
greater  the  abundance  of  rust  on  it,  and  the  larger  proportion  of  the  rust 
in  the  teleuto  stage. 

In  the  series  of  barleys,  the  three  older  plots  headed  in  42,  50,  and  50 
days  respectively.  The  fourth  put  out  a  few  heads  70  days  after  planting. 


218  AMERICAN   JOURNAL   OF    BOTANY  [Vol.  9 

The  last  two  sowings,  of  August  5  and  August  25,  never  reached  the  heading- 
out  stage.  The  barleys  were  rust-free  until  the  middle  of  September, 
when  a  few  uredo  pustules  were  to  be  discovered  on  the  leaves  and  sheaths 
of  the  three  older  plots.  No  teleuto  was  found. 

As  has  been  noted  for  the  plots  of  wheat  and  rye,  even  more  strikingly 
in  the  case  of  the  oats,  the  rate  of  development  of  the  parasite  differs  with 
the  host.  It  is  much  more  rapid  in  the  case  of  the  oats  than  in  that  of  the 
other  cereals.  For  example,  in  the  seedling  stage  the  amount  of  rust  on 
the  plants  may  appear  less  on  the  oats  than  on  the  rye  and  wheat,  although 
at  the  time  of  heading  out  the  same  plants  will  show  the  reverse  condition, 
the  oats  being  much  more  severely  infected. 

The  rust  history  of  plots  of  cereals  sown  at  successive  intervals  through 
the  summer  may  be  taken  as  indicating  that  the  age  and  maturity  of  the 
host  is  a  factor  in  the  progress  of  the  disease,  and  that  the  action  of  this 
factor  differs  with  the  identity  of  the  host  plant. 

LABORATORY  AND  GREENHOUSE  STUDIES 
Culture  Methods 

Four  cereal  rusts — Puccinia  coronifera  Kleb.,  P.  secalina  Grove,  P.  triti- 
cina  Eriks.,  and  P.  Sorghi  Schw. — were  successfully  grown  for  periods  of 
time  on  the  host  in  pots  on  greenhouse  benches  as  described  by  Melhus 
(1912)  and  Fromme  (1913),  and  under  aseptic  conditions  on  host  seedlings 
growing  in  test  tubes  as  described  by  Ward  (19020)  and  Mains  (1917). 
Variations  were  introduced  in  both  methods. 

Fromme  (1913)  reviews  the  problem  of  growing  cereal  rusts  in  the  green- 
house. The  method  recommended  by  him  includes  sowing  rust  spores  on 
new  host  plants  every  few  weeks  by  applying  them  with  a  scalpel  or  camel's 
hair  brush,  or  spraying  on  in  suspension  in  water  with  an  atomizer,  and 
then  putting  the  host  plants  into  a  moist  chamber  for  from  24  to  48  hours 
to  provide  the  conditions  of  high  humidity  necessary  for  spore  germination 
and  infection.  Tests,  however,  indicated  that  the  first  part  of  the  method 
recommended  by  Fromme,  artificially  sowing  rust  spores  on  the  new  host, 
was  not  necessary  under  the  conditions  obtaining  in  the  Columbia  green- 
house. It  was  found  that  when  new  host  plants  are  grown  beside  infected 
plants  in  the  greenhouse,  rust  spores  will  be  sown  on  them  by  natural 
agencies,  such  as  convection  and  other  atmospheric  currents,  sufficient  to 
produce  abundant  infection  if  conditions  of  high  humidity  are  provided 
occasionally  to  render  possible  the  germination  of  the  spores. 

Accordingly,  the  method  adopted  for  maintaining  stock  cultures  of  the 
cereal  rusts  in  the  greenhouse  was  to  introduce  new  host  plants  alongside 
the  infected  plants  every  third  week  and  to  cover  the  cultures  with  a  moist 
chamber  every  second  or  third  night.  The  fungus  maintained  itself  self- 
sown  in  this  manner,  and  no  artificial  inoculations  were  needed.  The 


May,  1922]  RAINES  —  VEGETATIVE   VIGOR   OF   THE   HOST  219 

advantage  of  such  a  method  of  maintaining  stock  cultures  of  cereal  rusts 
is  that  it  eliminates  the  most  technical  operation,  that  of  sowing  or  applying 
the  fungous  spores  to  the  new  host,  and  reduces  the  problem  of  maintaining 
cereal  rusts  in  culture  in  the  greenhouse  to  a  non-technical  routine  such  as 
can  be  entrusted  to  the  average  gardener  or  greenhouse  marh — 

In  growing  the  rust  under  aseptic  conditions  on  seedlings  in  test  tubes, 
the  method  developed  was  to  treat  the  seed  with  chlorine  water  (cf.  Wilson, 
1915),  put  the  seed  to  germinate  on  filter  paper  in  Petri  dishes,  and  transfer 
the  germinated  seed  to  a  test  tube  plugged  with  cotton.  Half  an  inch  of 
sterile  water  was  put  into  the  test  tube  with  the  plant.  The  reserve  food 
materials  of  the  endosperm  are  capable  of  bringing  the  seedling  to  the  third 
leaf  stage,  which  is  sufficient  to  raise  a  generation  of  the  rust  on  it.  P. 
coronifera  was  cultivated  for  10  generations  in  this  manner,  transfers  being 
made  once  a  month ;  P.  Sorghi  for  8  generations ;  P.  triticina  for  8  generations ; 
and  P.  secalina  for  6  generations.  A  small  platinum  spatula  was  employed 
for  making  transfers;  spores  were  applied  to  the  upper  surface  of  the  first 
leaf  in  each  case,  and  material  for  inoculum  was  taken  from  the  under 
surface.  That  a  cereal  rust  can  thus  be  grown  under  conditions  free  from 
accidental  contamination  was  indicated  by  the  total  absence  of  organic 
growth,  bacterial  or  fungous,  when  a  rust-infected  seedling  was  deposited 
on  sterile  beef-peptone  agar. 

Studies  on  the  Incidence  of  Infection  by  Measured  Doses  of  Uredospores 
of  Puccinia  Sorghi  on  Zea  Mays 

An  effort  was  made  to  determine  the  minimal  dose  of  uredospores  of 
P.  Sorghi  that  (i)  can  possibly,  and  (2)  will  certainly  produce  infection  in 
Zea  Mays.  191  tests  were  made  on  corn  seedlings  growing  under  aseptic 
conditions  in  twelve-inch  test  tubes. 

The  method  employed  to  determine  the  dose  and  to  inoculate  was  as 
follows:  A  dilute  suspension  of  uredospores  was  made  in  a  vial  of  sterile 
water.  A  small  drop  from  this  suspension  was  put  on  a  piece  of  sterile 
cover  slip,  and  the  number  of  uredospores  in  the  drop  was  counted  under 
the  microscope.  The  piece  of  cover  glass  was  then  inverted  and  deposited 
on  the  upper  surface  of  the  first  leaf  of  the  young  corn  seedling  in  the  test 
tube,  about  one  half  inch  below  the  tip,  bringing  the  drop  of  water  con- 
taining the  known  number  of  uredospores  in  contact  with  the  host  tissue. 
The  work  was  done  in  the  winter  in  the  laboratory,  with  no  rust  growing 
free  anywhere  in  the  building,  so  that  the  danger  of  accidental  contamina- 
tion was  negligible.  No  infection  ever  developed  on  the  seedlings  except 
on  the  spot  where  the  plant  had  been  inoculated. 

The  inoculated  seedlings  were  kept  under  observation  for  21  days. 
If  the  inoculated  leaf  yellowed  or  withered  before  15  days,  the  plant 
was  discarded.  The  data  on  191  tests  are  shown  in  table  4. 


220 


AMERICAN   JOURNAL   OF   BOTANY 


[Vol.  9 


TABLE  4 


No.  of 
Spores 

No.  of 
Inoculations 

No.  of 
Infections 

No.  of 
Spores 

No.  of 
Inoculations 

No.  of 
Infections 

I 

58 

2 

52 

O 

2 

18 

o 

53 

4 

O 

3 

6 

I 

55 

0 

4 

4 

0 

56 

o 

i 

10 
4 

0 
0 

57 
58 

I 

0 

7 

3 

o 

59 

I 

8 

5 

I 

61 

0 

9 

3 

I 

62 

0 

10 

6 

I 

63 

o 

ii 

2 

0 

64 

0 

12 

2 

0 

65 

o 

J3 

2 

I 

67 

0 

14 

2 

0 

68 

I 

16 

2 

I 

69 

o 

19 

I 

0 

72 

I 

22 

I 

o 

74 

o 

23 

I 

o 

77 

2 

25 

2 

2 

79 

o 

27 

I 

0 

86 

0 

28 

3 

I 

98 

o 

31 

I 

o 

IOO 

32 

I 

0 

103 

35 

I 

0 

104 

o 

36 

2 

I 

119 

40 

3 

0 

142 

42 

3 

0 

135 

44 

2 

0 

425 

47 

I 

0 

700 

48 

3 

0 

800 

' 

50 

i 

o 

1000 

The  results  cannot  be  considered  as  entirely  convincing  in  view  of  the 
many  factors  involved  in  a  successful  inoculation.  The  evidence  indicates, 
however,  that,  as  to  the  minimal  number  of  uredospores  which  can  possibly 
produce  infection,  it  is  possible  for  a  single  uredospore  to  produce  infection. 
In  each  of  the  two  cases  in  which  infection  was  produced  after  inoculation 
with  a  single  uredospore,  the  rust  appeared  after  the  usual  incubation  period 
as  a  very  small  pustule  at  the  point  of  inoculation.  In  one  case  the  in- 
fected leaf  withered  shortly  after  the  appearance  of  the  pustule;  in  the  other 
instance  the  mycelium  showed  normal  growth,  and  about  a  week  later 
seven  new  uredosori  were  produced  in  a  ring  around  the  first  pustule. 

As  regards  the  second  question,  the  minimal  dose  of  uredospores  which 
will  certainly  produce  infection,  the  data  indicate  this  to  be,  for  the  con- 
ditions under  which  the  work  was  done,  between  100  and  125.  This  is 
high.  In  view  of  the  varying  viability  of  spores  taken  at  one  time  from  the 
same  pustule,  and  of  their  further  variation  with  the  age  of  the  pustule, 
it  was  not  considered  possible  actually  to  test  the  germination  for  each 
sample  used.  However,  the  spores  were  always  taken  from  the  surface  of 
a  large  and  pulverulent  sorus,  and,  considering  that  the  index  of  germination 


May,  1922]  RAINES  —  VEGETATIVE   VIGOR   OF   THE   HOST  221 

of  the  uredospores  under  the  conditions  of  inoculation  was  from  75-90 
percent,  and  that  it  is  possible  for  a  single  spore  to  produce  infection,  we 
can  say  that  (taking  the  conservative  germination  figure  of  50  percent)  of 
more  than  fifty  spores  germinating  on  the  surface  of  the  leaf,  only  one 
produced  successful  infection.  Evidently,  successful  infection~by  a  uredo- 
spore  involves  other  factors  besides  that  of  germination  on  the  leaf  surface 
of  the  host  plant. 

The  Constitution  of  the  Fungous  Mycelium  as  a  Factor  in  Teleutospore 
Production  by  Puccinia  coronifera 

Our  knowledge  of  the  conditions  governing  teleutospore  production  in 
the  cereal  rusts  is  summarized  and  extended  by  Gassner  (1915),  who  con- 
siders that  the  determining  factor  is  the  physiological  aging  of  the  host 
tivssue,  teleutospore  production  being  particularly  coincident  with  the 
mobilization  of  the  food  resources  of  the  plant  for  flower  and  fruit  produc- 
tion. The  picture  of  teleutospore  production  presented  by  the  plants  of 
the  experimental  field  plots  described  above  closely  parallels  Gassner's 
observations  in  similar  experiments  and  is  consistent,  with  his  views. 

Consideration  of  the  behavior  of  Puccinia  coronifera  as  regards  teleuto- 
spore production,  when  grown  in  the  greenhouse,  leads  to  the  suggestion 
that  the  protoplasmic  constitution  of  the  fungous  mycelium  may  be  a  factor. 
Greenhouse  cultures  of  the  rust  from  material  brought  in  from  the  field  in 
the  vicinity  of  New  York  exhibited  moderate  teleutospore  production.  A 
series  of  cultures  from  material  sent  the  writer  by  J.I.  Durrell  from  Ames, 
Iowa,  on  the  other  hand,  grown  at  the  same  time  on  similar  host  material 
and  under  similar  conditions,  showed  very  abundant  teleutospore  produc- 
tion, the  difference  in  this  respect  between  the  two  series  of  cultures  being 
readily  noticeable.  While  such  teleutospore  production  on  potted  oat 
seedlings  in  the  greenhouse  is  more  commonly  on  the  older  infected  leaves, 
which  are  yellowing  at  the  tip,  it  is  not  unusual  to  observe  the  production  of 
teleutospores  by  rust  pustules  on  young  and  vigorous  leaves  shortly  after 
first  infection. 

Experiment  showed  that  it  is  readily  possible  to  secure  variation  in  the 
tendency  of  the  rust  towards  teleutospore  production  by  selection.  The 
rust  was  grown  in  test  tubes  under  aseptic  conditions.  Large  variation  in 
the  tendency  towards  teleutospore  production  was  noted  in  cultures  of  the 
third  generation,  some  rust  cultures  showing  no  teleutosori  at  all;  in  others 
as  much  as  75  percent  of  the  pustules  were  teleutosori.  Two  series  of 
cultures  were  therefore  propagated.  In  one  of  the  series,  transfers  were 
made  from  cultures  showing  no  teleutospores.  Of  36  cultures  in  this  series, 
20  showed  complete  absence  of  teleutosori ;  only  2  of  the  cultures  developed 
more  than  50  percent  of  the  winter  stage. 

In  the  second  series,  transfers  were  made  from  cultures  showing  75 
percent  teleutosori.  Of  35  cultures  in  this  series,  30  showed  more  than 


222 


AMERICAN   JOURNAL   OF   BOTANY 


[Vol.  9 


50  percent  teleutosori,  and  only  5  less  than  that.  Two  of  the  cultures  in 
this  series  never  produced  any  uredospores  whatever,  teleutosori  only  being 
developed.  It  was  obviously  impossible  to  make  transfers  from  such 
cultures. 

Figure  3,  Plate  XII,  shows  a  rust  mycelium  in  which  only  the  first 
pustule  produced  uredospores,  succeeding  pustules  bearing  only  teleuto- 
spores. 

Apparently  there  may  be  wide  differences  in  the  tendency  towards  the 
production  of  teleutospores  in  different  cultures  of  a  rust  fungus,  and  the 
factor  of  fungous  constitution  should  be  given  consideration  in  work  on 
the  conditions  of  teleutospore  production. 

Nutrition  and  Growth  Studies 

Water  Cultures 

Six  experiments  were  performed  with  Puccinia  Sorghi  on  corn  to  test 
the  effect  on  rust  development  of  growing  the  host  plants  in  culture  solu- 
tions of  varying  nutritive  value.  A  sugar  corn  was  used,  as  being  more 
susceptible  to  rust  than  a  flint  or  dent  corn.  The  seedlings  were  grown  in 
water  culture  in  25o-cc.  Erlenmeyer  flasks.  Knop's  nutrient  solution  was 
used  as  a  base.  Except  as  otherwise  noted,  the  endosperm  was  removed 
about  the  time  that  the  first  leaf  was  breaking  through  the  coleoptile,  so 
that  the  plant  was  entirely  dependent  for  sustenance  on  the  mineral  salts 
it  could  obtain  from  the  nutrient  solution  and  on  the  carbohydrates  it 
could  manufacture  in  its  leaf  tissue.  Inoculation  was  effected  by  spraying 
with  a  suspension  of  uredospores  and  covering  with  a  bell  jar  for  24  hours. 
Observations  were  made  on  the  incubation  period  and  on  the  progress  of 
the  disease  on  the  plants.  The  dry  weight  of  the  top  of  the  plant  at  the 
conclusion  of  the  experiment  was  taken  as  an  index  of  the  relative  vigor  of 
growth  of  the  plant. 

TABLE  5 
Exp.  i.     Effect  of  Renewing  Solution.     Plants  Inoculated  February  28,  1919. 


No.  of 

Treat- 

Dry Weight 
of  Top 

Observations 

Plant 

ment 

of  Plant 
inMg. 

March  9 

March  n 

March  13 

I  
2  

3  

Solution 
changed  once 
a  week 

Solution  not 
changed 

Solution  not 
changed 

340 
310 
280 

3    pustules  on 
third  leaf 

No  infection 
No  infection 

I     pustule    on 
second    leaf; 
3  pustules  on 
third  leaf 
i     pustule    on 
second  leaf 

No  infection 

2  pustules  on  second 
leaf;    3  pustules  on 
third  leaf 

i  pustule  on  first  leaf; 
4  pustules  on  second 
leaf;     i    pustule   on 
fourth  leaf 
i  pustule  on  first  leaf; 
I    pustule   on    third 
leaf 

May,  1922] 


RAINES  —  VEGETATIVE    VIGOR   OF   THE   HOST 


223 


Exp.  2.     Effect  of  Removing  Endosperm.     Plants  Inoculated  February  2$, 


No.  of 
Plant 

Treat- 
ment 

Dry  Weight 
of  Top 
of  Plant 
inMg. 

Observations 

March  9 

March  n 

March  13 

March  15 

I  

Endosperm  not 
removed 

Endosperm  re- 
moved 

Endosperm  re- 
moved; solution 
rendered   highly 
toxic    by    large 
excess  of  Fe2Cl6 

150 
80 
40 

3     pustules 
on       first 
leaf 
No      infec- 
tion 

No      infec- 
tion 

4     pustules 
on       first 
leaf 
i       pustule 
on  second 
leaf 
No      infec- 
tion 

4    pustules" 
on       first 
leaf 
i       pustule 
on  second 
leaf 
No      infec- 
tion 

5      pustules 
on        first 
leaf 
3      pustules 
on    second 
leaf 
No       infec- 
tion 

2      .     . 

3  

Exp.  j.     Effect  of  Culture  Solutions  of  Varying  Nutritive  Value.    Plants  Inoculated  March  19, 

IQIQ. 


No.  of 
Plant 

Treat- 
ment 

Dry  Weight 
of  Top 
of  Plant 
in  Mg. 

Observations 

March  25 

March  26 

March  27 

March  29 

I  

Full  nutrient  solu- 

1 60          Infection 

Infection 

13  pustules 

2pustuleson 

tion  ;  endosperm 

on  second 

on  second 

on  second 

first  leaf;  i 

not  removed 

and  third 

and  third 

leaf;         4 

pustule  on 

leaves 

leaves 

pustules 

second 

on     third 

leaf;  7  pus- 

leaf 

tules       on- 

third  leaf 

2  

Full  nutrient  solu- 

80 

No      infec- 

No     infec- 

3    pustules 

5      pustules 

tion 

tion 

tion 

on       first 

on        first 

leaf;         4 

leaf;          5 

pustules 

pust  ules 

on  second 

on    second 

leaf 

leaf 

3  

Full  nutrient  solu- 

80 

No      infec- 

No     infec- 

i      pustule 

3      pustules 

tion 

tion 

tion 

on       first 

on        first 

leaf;         2 

leaf;          4 

pustules 

pustules 

on  second 

on    second 

leaf;         i 

leaf;          2 

pustule 

pust  ules 

on     third 

on       third 

leaf 

leaf 

4....  . 

Nutrient  solution 

50 

No      infec- 

No     infec- 

2    pustules 

2      pustules 

rendered     toxic 

tion 

tion 

on  second       on    second 

with    excess    of 

leaf 

leaf;          I 

Fe2Cl6 

pustule  on 

third  leaf 

5  

Tap  water 

40 

No      infec- 

No     infec- 

i      pustule 

2      pustules 

tion 

tion 

on       first 

on        first 

leaf;         2 

leaf;          2 

pustules 

pustules 

on     third 

on    second 

leaf 

leaf;          i 

pustule  on 

third  leaf 

6  

Distilled  water 

2O 

No      infec- 

No     infec- 

No     infec- 

2   pustules 

tion 

tion 

tion 

on    second 

leaf 

7  

Highly  toxic   nu- 

2O 

No      infec- 

No     infec- 

No     infec- 

i pustule  on 

trient  solution 

tion 

tion 

tion 

first  leaf 

224 


AMERICAN  JOURNAL  OF  BOTANY 


[Vol.  9 


Exp.  4.     Effect  of  Varying  Concentration  of  Nutrient  Solution. 

1919 


Plants  Inoculated  April  2, 


No.  of 
Plant 

Concen- 
tration of 
Nutrient 
Solution 

Dry  Weight 
of  Top 
of  Plant 
in  Mg. 

Observations 

April  8 

April  9 

April  14 

I. 

0.012 
O.OO9 

O.OO6 
0.003 

0.0015 

Distilled 
water 

2O 
140 

no 

110 
100 

(d 

No  infection 
Rust    showing 
on  second  leaf 

No  infection 

Rust    showing 
on  third  leaf 

No  infection 
jst  roved) 

No  infection 
12  pustules  on 
second  leaf 

3   pustules  on 
second  leaf 
19  pustules  on 
second     leaf; 
10  pustules 
on  third  leaf 
No  infection 

No  infection;  plant  dying 
Large  number  of  pustules 
on    first,     second,     and 
third  leaves 
5  pustules  on  second  leaf; 
plant  dying 
5  pustules  on  first  leaf;  20 
pustules  on  second  leaf; 
10  pustules  on  third  leaf 

17  pustules  on  first  leaf; 
8  pustules  on  second  leaf 

2  

3  
4  

K  . 

6  

In  all  the  water-culture  experiments  (table  5)  an  increase  in  the  incuba- 
tion period  of  the  rust  with  depression  in  the  vigor  and  rate  of  growth  of  the 
host  plant  was  apparent.  Coincident  with  the  increased  incubation  period 
of  the  rust  on  host  plants  of  poor  growth  and  little  vigor  went  always  a 
marked  depression  in  the  luxuriance  of  the  fungus.  The  pustules  were 
appreciably  smaller,  and  produced  decidedly  fewer  spores. 

Comparing  the  incubation  period  of  the  rust  on  the  leaves  of  the  same 
plant,  it  is  found  to  be  shorter  on  the  younger  leaves.  Comparing  the 
first  and  second  leaves,  we  find : 

Infection  noted  on  the  first  leaf  before  it  appeared  on  second  leaf.  .  .  .  o 

Infection  noted  simultaneously  on  first  and  second  leaves 5 

Infection  noted  on  second  leaf  before  first 7 

Infection  on  first  leaf;  none  on  second 2 

Infection  noted  on  second  leaf;  none  on  first 7 

The  older  host  tissue,  it  would  seem,  provided  a  less  congenial  environ- 
ment for  the  development  of  the  rust. 

Incidental  to  the  above-described  water-culture  experiments  was  the 
demonstration  of  the  ability  of  the  rust  to  develop  on  chlorotic  tissue. 
Some  corn  seedlings  were  grown  in  iron-free  nutrient  solution,  and  the 
fourth  and  fifth  leaves  produced  by  the  plants  were  completely  blanched. 
The  plants  were  sprayed  with  a  spore  suspension  to  test  the  susceptibility 
of  these  leaves  to  the  rust.  Nine  days  after  inoculation  the  chlorotic  leaves 
showed  abundant  rust  infection.  Giddings  (personal  communication) 
has  obtained  infection  with  Gymno  sporangium  juniperi-virginianae  on  apple 
leaves  blanched  by  being  kept  in  the  dark  room  while  unfolding  from  the 
bud.  It  may  be  concluded  that  the  presence  of  chlorophyll  is  not  a  neces- 
sary condition  for  rust  development. 


May,  1922]  RAINES  —  VEGETATIVE   VIGOR   OF   THE   HOST  225 

Soil  Cultures 

From  the  studies  of  Sheldon,  Ward,  and  Stakman,  as  also  from  the 
experiments  described  above,  it  may  be  considered  as  established  that, 
within  the  range  of  forms  worked  with,  conditions  unfavorable  to  the 
growth  of  the  host  cause  an  increase  in  the  incubation  period  of  the  rust  and 
depress  the  luxuriance  of  growth  of  the  fungous  mycelium  as  indicated  by 
the  size  of  the  pustules  and  the  number  and  size  of  the  spores  produced 
in  them. 

Concerning  the  effect  of  conditions  unfavorable  to  the  growth  of  the 
host  on  the  incidence  of  rust  infection — the  number  of  successful  infections 
produced  on  a  unit  area  of  host  tissue  by  a  given  dose  of  inoculum — our 
knowledge  must  be  regarded  as  not  so  definite.  The  data  extant  are  sub- 
ject to  criticism  because  of  the  relatively  small  number  of  variables  studied 
and  because  of  the  irregularity  of  dosage  inherent  in  the  method  of  inocula- 
tion employed.  Ward  (1902)  applied  spores  to  the  leaf  by  means  of  a 
swab  of  cotton,  and  Stakman  (1914,  p.  n)  employed  a  flat  inoculating 
needle  for  this  purpose. 

Studies  on  the  relation  between  host  vigor  and  incidence  of  infection, 
to  be  of  critical  value,  must  be  made  with  numbers  of  variables  sufficient 
to  preclude  undue  distortion  of  the  results  by  fluctuations  in  condition  of 
host  and  fungus,  and  by  errors  in  the  taking  and  studying  of  data;  the 
method  of  inoculation  employed  must  stand  criticism  as  to  the  uniformity 
of  dosage  for  the  variables  compared;  and,  if  any  but  the  grossest  relations 
between  the  variables  studied  are  to  be  made  apparent,  a  more  exact  basis 
than  visual  observation  and  judgment  must  be  employed  for  determining 
vigor  of  growth  of  host  plant  and  degree  of  rust  infection  on  it. 

In  the  experiments  described  below  on  the  relation  between  host  vigor 
in  the  oat  plant  and  its  susceptibility  to  crown  rust,  data  were  obtained  on 
1450  individual  plants  receiving  different  nutritive  treatment  and  exhibiting 
wide  variation  in  vigor  of  growth.  The  plants  were  grown  in  pots  in 
the  greenhouse.  Inoculation  was  effected  under  natural  field  conditions 
by  placing  the  pots  containing  the  experimental  plants  out  of  doors  near  a 
stand  of  oats  heavily  infected  with  crown  rust.  Analysis  of  the  data  indi- 
cates that  the  dosage  for  the  variables  compared  was  uniform.  The  experi- 
ments were  concluded  and  the  readings  taken  before  the  rust  on  any  of  the 
plants  approached  the  maximum  that  the  leaf  tissue  could  support,  so 
that  the  infection  present  at  the  time  may  be  considered  an  index  of  the 
response  of  the  host  tissue  to  the  conditions  of  inoculation  to  which  it  was 
subjected,  and  variation  in  this  response  between  host  tissues  receiving 
similar  doses  of  inoculum  was  presumably  due  to  differences  in  the  condi- 
tion of  the  tissues  compared. 

Values  for  the  vigor  of  the  host  plant  and  for  the  amount  of  rust  in- 
fection present  on  it  were  obtained  as  follows:  At  the  conclusion  of  the 
experiment  the  plant  was  cut  off  at  the  base  and  observations  were  taken 


226 


AMERICAN   JOURNAL  OF   BOTANY 


[Vol.  9 


of  the  number  of  rust  pustules  on  the  upper  surface  of  each  leaf,  of  the 
length  of  each  leaf  in  inches,  of  the  extreme  length  of  the  entire  plant,  and 
of  the  number  of  stools  it  had  produced.  The  plant  was  then  dried,  and 
its  dry  weight  was  obtained.  The  dry  weight  of  the  plant  was  adopted 
as  the  index  of  its  relative  vigor  of  growth,  because  it  makes  possible  more 
accurate  seriation  of  the  variables  on  this  value  than  an  index  such  as  the 
height  of  the  plant  or  the  total  leaf  length. 

As  an  index  of  the  degree  of  infection  of  the  plant  the  value  adopted 
was  the  number  of  pustules  on  an  average  unit  area  of  the  most  severely 
infected  leaf — calculated  by  dividing  the  number  of  rust  pustules  on  the 
leaf  by  the  length  of  the  leaf  in  inches,  and  by  its  width  at  the  base  in  six- 
teenths of  an  inch.  This  value  was  found  to  have  a  positive  correlation 
(r  =  .7803  =b  .0167  for  the  250  variables  of  experiments  I,  II,  and  III) 
with  the  value  that  at  first  thought  would  seem  most  desirable:  namely, 
the  total  number  of  rust  pustules  counted  on  the  leaves  of  the  plant,  divided 
by  the  total  leaf  length  in  inches,  and  by  the  largest  leaf  width  in  sixteenths 
of  an  inch — and  is  preferable  for  adoption  in  work  of  this  kind  not  only 
because  it  is  easier  to  obtain,  but  also  because  it  avoids  the  error  introduced 
by  the  development  of  new  leaf  surface  during  the  incubation  period.  The 
most  highly  infected  leaf  on  the  plant  was  usually  the  lowest  leaf  in  good 
condition.  In  tables  6-10  both  values  are  given. 

Experiment  I 

66  oat  plants  were  grown  in  soil  in  2-inch  pots,  divided  into  three  groups 
on  the  basis  of  the  number  of  plants  grown  to  a  pot.  The  soil  was  a  rich 
garden  loam.  The  seed  was  sown  July  6,  1920,  three  grains  being  put 
into  the  soil  for  every  plant  desired,  and  the  seedlings  were  later  thinned  out 
to  the  number  of  plants  desired.  The  pots  were  kept  on  a  bench  in  the 
greenhouse  until  August  n,  when  they  were  taken  out  of  doors  and  set 
near  a  patch  of  rusty  oats,  subjecting  the  plants  to  natural  conditions  of 
inoculation  and  infection.  The  experiment  was  concluded  on  August  24. 
The  data  on  this  experiment  are  given  in  table  6. 

TABLE  6 


Mean 

Mean  No.  of 

Mean  No.  of 

No.  of 

No.  of 

Dry  Weight 

Pustules 

Pustules 

Group 

Variables 

Plants  to  a 
2-inch  Pot 

of  Top  of 
Plant 

per  Ave.  Unit 
Area  of  Total 

per  Ave.  Unit 
Area  of  most  Severely 

in  Mg. 

Leaf  Surface 

Infected  Leaf 

a 

23* 

5 

6l 

I.I 

4.2 

b 

18 

2 

135 

2.1 

6.0 

c 

25 

I 

183 

2-3 

6.1 

Experiment  II 

70  plants  were  grown  in  3-inch  pots,  divided  into  three  groups  on  the  basis 
of  the  number  of  plants  grown  to  a  pot.     Soil,  method  of  seeding,  and  dates 
*  Plus  2  destroyed. 


May,  1922] 


RAINES  —  VEGETATIVE   VIGOR   OF   THE    HOST 


227 


of  sowing,  setting  out  of  doors  to  be  inoculated,  and  of  concluding  the  experi- 
ment were  the  same  as  in  experiment  I  described  above.  The  results  are 
shown  in  table  7. 

TABLE  7 


Mean 

Mean  No.  of 

Mean  No.  of 

No.  of 

No.  of 

Dry  Weight 

Pustules 

Pustules 

Group 

Variables 

Plants  to  a 
3-inch  Pot 

of  Top  of 
Plant 

per  Ave.  Unit 
Area  of  Total 

per  Ave.  Unit 
Area  of  most  Severely 

in  Mg. 

Leaf  Surface 

Infected  Leaf 

a 

25 

5 

96 

1.6 

4.1 

b 

20 

2 

264 

i-7 

4.8 

c 

25 

I 

407 

2.O 

5-2 

Experiment  III 

12 o  plants  were  grown  in  4^-inch  pots,  divided  into  four  groups  on  the 
basis  of  the  number  of  plants  grown  to  a  pot.  Soil,  method  of  seeding,  and 
dates  of  sowing,  of  setting  out-doors  to  be  inoculated,  and  of  concluding  the 
experiment  were  the  same  as  in  experiment  I.  Results  are  given  in  table  8. 

TABLE  8 


Mean 

Mean  No.  of 

Mean  No.  of 

No.  of 

No.  of 

Dry  Weight 

Pustules 

Pustules 

Group 

Variables 

Plants  to  a 
4^-inch  Pot 

of  Top 
of  Plant 

per  Ave.  Unit 
Area  of  Total 

per  Ave.  Unit 
Area  of  most  Severely 

in  Mg. 

Leaf  Surface 

Infected  Leaf 

a 

50 

IO 

161 

1-5 

3-6 

b 

25 

5 

352 

2.4 

6.4 

c 

2O 

2 

66  1 

2.7 

6-5 

d 

25 

I 

976 

2-5 

6.2 

i 

Experiment  IV 

600  oat  plants  were  grown  in  4^-inch  pots,  5  plants  to  a  pot;  15  grains 
being  planted  in  each  pot  in  the  first  place,  and  the  young  seedlings  thinned 
out  to  the  desired  number.  The  plants  were  divided  into  six  groups  of 
100  individuals  each  on  the  basis  of  soil  composition  and  treatment,  as 
follows : 

Group  A :   Soil  composed  of  sand  only. 

Group  B:   Soil  a  mixture  of  i  sand  and  3-  garden  loam. 

Group  C:   Soil  a  mixture  of  i  sand  and  ^  garden  loam. 

Group  D:  Soil  the  same  mixture  as  in  Group  C.  In  addition,  KC1  at  the  rate  of  350 
pounds  to  the  6-inch  acre  of  2,000,000  pounds  was  intimately  mixed  with  the  soil. 

Group  E:  Soil  the  same  mixture  as  in  Group  C.  In  addition,  acid  phosphate  at  the 
rate  of  750  pounds  to  the  acre  was  intimately  mixed  with  the  soil. 

Group  F:  Soil  the  same  mixture  as  in  Group  C.  In  addition,  sodium  nitrate  at  the 
rate  of  500  pounds  to  the  acre  was  intimately  mixed  with  the  soil. 

Seed  was  sown  July  n,  1920.  On  July  24,  July  31,  and  August  7  the 
plants  of  groups  Z),  £,  and  F  had  additional  quantities  of  fertilizer  applied 


228 


AMERICAN   JOURNAL   OF   BOTANY 


[Vol.  9 


in  water  solution  at  the  rate  of  100  pounds  to  the  acre.  On  August  9  the 
plants  were  placed  out  of  doors  to  be  inoculated.  The  experiment  was  con- 
cluded on  August  27.  Figures  I  and  2,  Plate  XI,  illustrate  the  growth 
differences  obtained  between  the  plants  of  the  different  groups  in  these 
experiments. 

In  table  9,  the  groups  are  arranged  in  order  of  the  vigor  of  growth  ex- 
hibited by  the  plants. 

TABLE  9 


Mean 

Mean  No.  of 

Mean  No.  of 

No.  of 

Soil 

Dry  Weight 

Pustules 

Pustules 

Group 

Variables 

Treatment 

of  Top 
of  Plant 

per  Ave.  Unit 
Area  of  Total 

per  Ave.  Unit 
Area  of  most  Severely 

in  Mg. 

Leaf  Surface 

Infected  Leaf 

A 

100 

sand 

120 

.6 

2.0 

E 

100 

acid 

155 

.8 

2.7 

phosphate 

B 

100 

$  sand 

20O 

•7 

2-3 

D 

IOO 

KC1 

2O2 

I.O 

3-2 

C 
F 

IOO 
IOO 

\  sand 
NaNO3 

341 

564 

•9 

1.2 

3-i 

4-5 

Experiment  V 

This  was  a  duplicate  of  Experiment  IV,  started  a  week  later.  The  seed 
was  sown  July  17,  the  plants  were  placed  out  of  doors  to  be  inoculated 
August  10,  and  the  experiment  was  concluded  August  31.  The  results  are 
shown  in  table  10. 

TABLE  10 


Mean 

Mean  No.  of 

Mean  No.  of 

No.  of 

Soil 

Dry  Weight 

Pustules 

Pustules 

Group 

Variables 

Treatment 

of  Top 

per  Ave.  Unit 

per  Ave.  Unit 

of  Plant                 Area  of  Total 

Area  of  most  Severely- 

in  Mg.                    Leaf  Surface 

Infected  Leaf 

A 

IOO 

sand 

47 

5-1 

11.6 

B 

IOO 

£  sand                 53 

5-1 

11.8 

E 

IOO 

acid                    93 

5-2 

H-3 

phosphate 

C 

IOO 

£  sand 

93 

4.5 

9-5 

D 

IOO 

KC1 

96 

4.4 

10.2 

F 

IOO 

NaNO3              359 

3-i 

7.6 

Relation  between  Host  Vigor  and  Pustule  Size 

In  all  five  of  the  soil-culture  experiments  there  was  evident  a  marked 
decrease  in  the  size  of  the  rust  pustules  on  the  host  plants  the  growth  rate 
of  which  was  depressed.  The  lengths  of  100  contiguous  pustules  on  plants 
from  groups  a  and  c  of  experiment  I;  groups  a  and  c  of  experiment  II; 
groups  a  and  d  of  experiment  III;  groups  A  and  F  of  experiment  IV;  and 
groups  A  and  F  of  experiment  V  were  found  to  fall  into  the  following 
classes ; 


May,  1922]  RAINES  —  VEGETATIVE    VIGOR   OF   THE    HOST 

TABLE  n 


229 


Experiment 

I 

II 

III 

IV                    V 

\ 

Group 

Group 

Group 

Group 

Group 

a 

c 

a 

c 

a 

d 

A 

F 

A 

F 

No.  of  pustules  |  mm.  long  
i  mm 

94 
6 

20 
20 

34 
24 

2 

72 
28 

H 

>! 

4 

2 

82 
18 

22 
30 
30 
12 

4 

2 

96 

4 

12 
30 
46 
8 

4 

70 
25 
3 

2 

8 
24 
24 
34 

7 
3 

i£  mm.  
2  mm 

2\  mm.  
3  mm. 

Sum  of  lengths  of  100  pustules  in  mm. 

53 

134 

64 

130 

59 

126 

52 

131 

68 

169 

Figures  4  and  5  of  Plate  XII  illustrate  the  relative  size  of  the  pustules 
on  leaves  of  semi-starved  and  of  vigorously  growing  plants. 

Pustules  attained  a  larger  size  on  the  more  rapidly  growing  host  plants, 
indicating  that  a  more  luxuriant  host  tissue  means  a  more  luxuriant  parasitic 
mycelium. 

DISCUSSION 
Relation  between  Host  Vigor  and  Incidence  of  Infection 

On  their  face  the  figures  obtained  in  the  soil-culture  experiments  indicate 
that  in  experiments  I,  II,  III,  and  IV  there  occurred  a  decreased  incidence 
of  infection  with  depression  in  growth  vigor  of  the  host;  but  in  experiment  V 
the  figures  indicate  quite  as  definitely  precisely  the  opposite  relation — 
namely,  increased  incidence  of  infection  with  depression  in  the  growth 
rate  of  the  host. 

The  dosage  for  all  six  groups  of  variables  in  soil-culture  experiments 
IV  and  V  was  probably  essentially  the  same.  The  plants  were  arranged  in 
order  of  alphabetical  designation  of  the  groups:  A,  B,  C,  D,  E,  F.  The 
possibility  might  be  suggested  that  in  experiment  IV  inoculation  proceeded 
from  the  direction  of  F  and  that  the  plants  from  F  to  A  were  subjected  to 
progressively  diminishing  doses  of  inoculum;  and,  conversely,  that  in 
experiment  V  inoculation  was  from  the  direction  of  A  and  that  the  plants 
from  A  to  F  received  progressively  diminishing  doses  of  uredospores.  This 
would. make  the  amount  of  infection  observed  on  the  plants  of  the  different 
groups  a  function  of  their  positions  relative  to  each  other.  But  actually 
the  amount  of  infection  observed  is  correlated  not  with  the  position  of  the 
group  but  with  its  relative  growth  vigor  as  indicated  by  the  mean  dry 
weight  of  the  plants.  Thus,  in  both  experiments  IV  and  V,  group  E  exhibits 
an  amount  of  infection  not  like  group  F,  next  to  which  it  was  placed,  but 
like  group  B  which  it  resembles  in  vigor  of  growth.  We  may  conclude  that 


230 


AMERICAN   JOURNAL    OF   BOTANY 


[Vol.  9 


the  dosage  for  the  variables  compared  in  any  experiment  was  uniform  and 
that  the  variation  in  the  amount  of  rust  observed  on  the  different  groups 
of  plants  in  the  experiment  is  due  to  differences  in  the  reactions  of  the  plant 
tissue  to  the  infection  to  which  they  were  subject. 

The  explanation  of  the  apparent  reversal  of  the  result  in  soil-culture 
experiment  V  as  compared  with  the  others  is  probably  to  be  found  in  the 
age  of  the  plants  and  in  the  length  of  time  they  were  exposed  to  infection. 
The  experiments  are  compared  in  table  12. 

TABLE  12 


Experiment 

I 

II 

in 

IV 

v 

Age  of  plants  at  conclusion  of  experiment  (days) 
Age  of  plants  when  set  out  of  doors  to  be  in- 
oculated   

49 

^5 

49 

35 

49 

T.SL 

47 
*l 

45 
24 

Number  of  days  out  of  doors  and  exposed  to 
infection  

15 

15 

15 

16 

21 

Number  of  variables 

66 

7O 

I2O 

600 

6OO 

Average  dry  weight  of  top  of  plants  (mg  ) 

127 

278 

518 

26/L 

123 

Average  infection  (total  leaf  surface)  
Average  infection  (most  severely  infected  leaf)  .  . 

1.8 
54 

1.8 
4-7 

2.3 
5-7 

•9 
3-0 

4.6 
10.4 

Experiment  V  differs  from  the  other  four  experiments  in  that  (i)  when 
set  out  of  doors  to  be  inoculated  the  plants  were  from  7  to  1 1  days  younger. 
Even  at  the  conclusion  of  the  experiment  these  plants  had  only  half  the 
dry  weight  of  the  plants  of  experiment  IV  and  were  evidently  much  less 
mature.  (2)  When  the  experiment  was  concluded  the  plants  had  been 
out  of  doors  and  subject  to  infection  6  days  longer.  If  we  allow  an  incuba- 
tion period  of  10  days  for  the  rust,  then  the  rust  present  on  the  plants  of 
experiment  V  at  the  conclusion  of  the  experiment  represents  inoculation 
through  a  period  of  time  twice  as  long  as  in  the  case  of  the  other  experiments. 
(3)  The  amount  of  rust  on  the  plants  at  the  conclusion  of  the  experiment  was 
several  times  greater  in  experiment  V  than  in  any  of  the  other  experiments. 

The  last-mentioned  fact  immediately  brings  into  view  an  aspect  of  the 
method  of  experimentation  used  tending  to  limit  the  value  of  the  pustule 
count  as  a  criterion  of  the  frequency  of  penetration  and  infection  by  the 
uredospore  germ  tube.  It  is  probable  that  only  in  cases  of  very  sparse 
infection  is  there  a  pustule  for  every  focus  of  infection,  and  that  only  in 
cases  of  very  sparse  infection  is  the  number  of  pustules  counted  an  accurate 
index  of  the  number  of  infections  which  have  taken  place.  With  abundance 
of  infection  there  appears  a  tendency  for  the  coalescence  of  foci  of  infection, 
for  two  or  more  mycelia  the  result  of  contiguous  infections  to  coalesce  and 
produce  only  one  pustule;  and  this  tendency  would  be  highly  accentuated 
on  the  more  vigorously  growing  host  plants  where  the  parasite  finds  a 
favorable  nidus  and  develops  more  luxuriantly.  In  experiment  V  the 
error  introduced  by  the  coalescence  of  mycelia  may  well  have  masked  a 


May,  1922] 


RAINES VEGETATIVE   VIGOR   OF   THE   HOST 


231 


higher  incidence  of  infection  in  the  vigorously  growing  plants  of  group  F 
and  have  converted  it  into  an  apparently  lower  susceptibility.  It  is  notice- 
able that  the  pustules  were  larger  in  experiment  V  than  in  the  other  four 
experiments. 

Variation  in  the  Incidence  of  Rust  Infection  with  Variation  in  the  Growth 
Vigor  of  the  Host  Plant,  due  to  Constitutional  or  Racial  Differences 

In  soil-culture  experiments  IV  and  V,  when  the  100  variables  of  each 
group  were  arranged  in  order  of  dry  weight,  the  series  divided  into  five 
equal  parts  of  20  variables  each,  and  the  average  weights  and  degrees  of 
infection  of  these  sub-groups  determined,  a  certain  relation  was  apparent 
between  the  relative  weight  attained  by  a  plant  and  the  incidence  of  rust 
infection  on  it.  The  figures  obtained  in  this  analysis  of  the  data  are  pre- 
sented in  table  13. 

TABLE  13 

Experiment  I V 


Mean  Dry  Weight  of  Tops  of 

Mean  Infection  per  Unit  Area  of  most 

Plants  in  Mg. 

Severely  Infected  Leaf  of  Plant 

Group 

Sub-groups 

First 

Second 

Third        Fourth 

Fifth 

First 

Second 

Third 

Fourth 

Fifth 

A.... 

40 

65 

110 

148          239 

2.3 

2.4 

1.8 

2.O 

1.6 

E...  . 

99 

129 

I48 

172          231 

2.8 

2.1 

2.9 

3-5 

2.1 

B.... 

99 

140 

179 

231          345 

2.3 

2.9 

2-5 

2.1 

1.8 

D.... 

90 

144 

182 

231          363 

3-6 

3-0 

2-5 

3-9 

2.9 

c.... 

141 

233 

336 

430 

596 

4.0 

3-0 

2-3 

44 

1.7 

F.... 

305 

450 

555 

653 

812 

4-7 

57 

5-2 

3-8 

3-3 

129 

193 

252 

3ii 

431 

3-3 

3-2 

2-9 

3-3 

2.2 

Experiment  V 


Mean  Dry  Weight  of  Tops  of 

Mean  Infection  per  Unit  Area  of  most 

Plants  in  Mg. 

Severely  Infected  Leaf  of  Plant 

Group 

Sub-groups 

First 

Second 

Third 

Fourth 

Fifth 

First 

Second 

Third 

Fourth 

Fifth 

A.. 

21 

34 

43 

54 

83 

n.8 

13-6 

H.5 

1  1.  6 

9-3 

B.... 

22 

36 

50 

65 

92 

12.3 

14.0 

11.7 

12.2 

8.6 

E.... 

42 

67 

85 

1  08 

159 

15-9 

12.2 

11.9 

8.6 

7.8 

C.... 

53 

71 

88 

106 

148 

IO.2 

IO.O 

II.  O 

8.6 

74 

D.... 

47 

72 

90 

107 

162 

12.  0 

13.2 

10.5 

8.0 

7.2 

F.  .  .  . 

190 

283 

349 

416 

558 

9-9 

6.8 

7-2 

7-7 

6.2 

63 

94 

118 

. 

143 

200 

12.0 

n.6 

10.6 

9-5 

7-8 

The  figures  show  that  there  was  considerable  variation  in  the  growth 


232  AMERICAN  JOURNAL  OF   BOTANY  [Vol.  9 

attained  by  plants  receiving  the  same  treatment,  and  that  the  larger  plants 
were  less  susceptible  to  rust  infection — increased  resistance  being  par- 
ticularly marked  in  the  sub-group  including  the  largest  of  the  plants. 

The  seed  employed  was  a  commercial  " Swedish  Select"  oats  in  which 
we  should  expect  a  mixture  of  strains  as  regards  rate  of  growth,  speed  of 
maturity,  and  susceptibility  to  rust.  In  view  of  the  uncertainty  as  to 
the  varietal  purity  of  the  seed  employed,  the  differences  in  incidence  of 
rust  infection  on  plants  receiving  the  same  treatment  and  showing  differences 
in  vigor  of  growth  are  probably  indicative  of  constitutional  differences  in 
susceptibility  to  rust  which  may  be  correlated  with  similar  constitutional 
differences  in  speed  of  growth;  and  so  may  be  considered  as  not  necessarily 
bearing  on  the  main  problem  I  am  considering,  which  is  concerned  with 
the  effect  on  rust  susceptibility  of  externally  induced  variations  in  the 
vegetative  vigor  of  the  host.  The  establishment  of  an  inverse  relation 
between  susceptibility  to  rust  and  speed  of  growth  in  oat  varieties  would 
lend,  however,  new  significance  to  the  practical  injunction  of  the  agrono- 
mists to  plant  early-maturing  varieties  of  oats  in  order  to  escape  loss  from 
rust,  indicating  that  selection  of  rapidly  growing  and  early-maturing  strains 
of  oats  automatically  implies  selection  for  rust  resistance  as  well. 

The  Possibility  of  a  Direct  Relation  between  Environmental 
Conditions  and  Rust  Resistance 

Groups  D,  E,  and  F  in  experiments  IV  and  V  were  intended  as  tests  for 
a  possible  direct  effect  on  rust  susceptibility  of  specific  nutrient  substances — 
that  is,  an  effect  independent  of  variations  in  the  health  and  vigor  of  the 
host  plant.  A  potash  fertilizer  was  applied  to  the  plants  of  group  D\  a 
phosphate  fertilizer  to  those  of  group  E\  and  the  plants  of  group  F  were 
richly  fed  with  a  nitrogen  salt. 

The  infection  observed  in  these  groups  is  in  no  instance  so  far  different 
from  that  on  plants  of  similar  weight  in  the  groups  not  treated  with  any 
special  fertilizer  as  to  justify  the  inference  that  the  fertilizing  chemicals 
were  exerting  any  influence  on  the  rust  resistance  of  the  host  other  than  is 
implied  in  their  effect  on  the  general  condition  and  vigor  of  the  plant. 

In  experiment  IV  the  potash  and  phosphate  applications  proved  ex- 
cessive, and  the  growth  of  the  plants  was  appreciably  retarded  as  compared 
with  the  plants  of  group  C\  in  experiment  V  the  potash  and  phosphate 
fertilizers  had  no  effect  on  the  growth  of  the  plants.  In  both  experiments 
the  potash-  and  phosphate-fertilized  plants  show  a  somewhat  higher  in- 
cidence of  infection  than  plants  of  similar  weight  not  treated  with  special 
fertilizers;  a  tendency  at  variance  with  the  statements  of  Bolley  (1889,  p.  18) 
and  Spinks  (1913.  P-  247)  that  these  fertilizers  give  increased  rust  resistance. 
In  group  F  the  stimulating  action  of  the  nitrate  fertilizers  on  the  growth  of 
the  host  was  so  marked  that  there  can  be  no  hesitation  in  referring  the 
increased  susceptibility  observed  to  this  effect  rather  than  to  any  direct 


May,  1922]  RAINES  —  VEGETATIVE   VIGOR  OF   THE   HOST  233 

action  of  the  chemical.  This  aspect  of  the  soil-culture  experiments  may 
be  considered  as  in  agreement  with  the  suggestion  arrived  at  in  the  biblio- 
graphical review  that  it  is  questionable  whether  a  direct  relation  between 
any  environmental  factor,  either  physical  or  chemical,  of  the  nature  of  a 
nutrient  or  a  stimulus,  and  susceptibility  to  rust,  has  been  established  in  the 
case  of  the  cereal  grains. 

Vegetative  Vigor  of  the  Host  as  a  Susceptibility-  and  Resistance-factor 

in  Infectious  Diseases 

Increased  susceptibility  with  increased  vigor  of  the  host,  in  plant 
diseases,  is  not  confined  to  the  rusts.  Marchal  (1902)  found  that  infection 
of  lettuce  by  Bremia  lactucae  was  favored  by  nitrogen  and  phosphates  and 
retarded  by  an  excess  of  potash.  Jones  (1905,  p.  38)  mentions  that  high 
fertilization,  especially  with  nitrogenous  manures,  lowers  the  powers  of 
the  potato  plant  to  resist  blight  and  rot.  McCue  (1913,  p.  18)  observed 
that  tomato  plants  treated  with  phosphatic  fertilizers  developed  less  leaf 
blight  than  control  plants,  while  plants  on  nitrogen  and  potash  plots  which 
at  the  same  time  gave  the  highest  yields,  indicating  greatest  vigor  of  growth, 
were  more  heavily  infected  than  the  controls.  Peltier  (1918)  has  observed 
with  the  citrus  canker,  and  Fromme  and  Murray  (1919,  p.  227)  with  the 
angular  leaf  spot  of  tobacco  ("the  development  of  the  organism  within  the 
tobacco  leaf  is  apparently  dependent  to  a  marked  degree  on  those  pre- 
disposing factors  which  promote  a  rapid,  vigorous  growth  of  the  host"), 
that  infection  is  heavier  under  conditions  which  favor  the  growth  of  the 
host.  Thomas  (1921)  obtained  evidence  of  increased  resistance  to  leaf 
spot  (Septoria  Apii)  of  celery  plants  the  vitality  of  which  was  depressed 
as  a  result  of  infestation  of  the  root  system  by  nematodes ;  and  of  decreased 
resistance  in  plants  richly  fed.  And  Levine  (1921)  has  observed  that  crown 
gall  on  beets  developed  more  rapidly  and  to  larger  size  on  roots  grown  in  a 
highly  manured  soil. 

While  the  claim  that  increased  vigor  of  the  host  means  greater  sus- 
ceptibility to  an  infection  may  appear  somewhat  anomalous  from  the  point 
of  view  of  current  theories  regarding  the  infectious  diseases,  observations 
such  as  form  the  subject  of  the  present  paper  are  readily  understood  when 
we  consider  the  infectious  diseases  in  the  light  of  the  larger  class  of  biological 
phenomena  of  which  they  are  an  artificially  selected  group — namely, 
parasitism,  commensalism,  and  symbiosis,  the  class  of  biological  phenomena 
in  which  one  organism  lives  within,  and  derives  its  sustenance  from,  the 
tissues  of  another  living  organism.  In  each  of  the  four  main  groups  of 
parasitic  organisms — the  bacteria,  the  protozoa,  the  worms,  and  the  fungi— 
a  series  of  intergradations  are  to  be  observed  in  the  physiological  interrela- 
tions of  host  and  parasite,  from  the  unceasing  and  violent  struggle  that 
continues  until  the  destruction  of  one  or  other  of  the  principals,  to  a  relation 
of  a  more  benign  type  characterized  by  great  subordination  and  even  tend- 


234  AMERICAN   JOURNAL   OF   BOTANY  [Vol.  9 

ency  to  usefulness  on  the  part  of  the  parasitic  organism,  and  by  the  utmost 
tolerance  on  the  part  of  the  host.  In  many  instances  the  nature  of  the 
reaction  is  not  constant,  but  varies  with  the  progress  of  the  host-parasite 
relation.  In  this  intergrading  series  of  possible  host-parasite  relations,  the 
inverse  relation  between  host  vigor  and  parasite  virulence  obtains  only  in 
the  instances  and  phases  where  the  reaction  of  the  host  to  the  parasite  is 
one  of  active  antagonism;  here  a  more  vigorous  host  means  a  host  of  greater 
physiological  capacity  to  combat  the  progress  of  the  invader.  But  when 
the  relation  between  host  and  parasite  is  of  a  symbiotic  type,  a  more  vigorous 
host  means  a  host  in  which  more  food  is  available  for  the  development  of 
the  parasite.  Because,  of  the  general  class  of  parasitological  phenomena, 
the  instances  mainly  in  the  field  of  pathological  interest  (the  diseases 
ordinarily  so  called)  are  an  artificially  selected  group  in  which  relations  of 
violent  antagonism  between  host  and  invading  organism  are  most  promi- 
nently in  evidence,  thought  in  the  field  of  pathology  has  developed  with  the 
physiological  antagonism  of  host  and  parasite  as  its  basal  concept;  and  the 
theories  of  immunity  extant  are  largely  concerned  with  the  nature  of  the 
antagonistic  reactions. 

In  the  group  of  the  fungi  the  transition  from  violent  and  destructive 
parasitism  to  parasitism  of^the  symbiotic  type  is  accompanied  by  a  transi- 
tion from  facultative  to  obligate  parasitism,  as  if  the  physiological  corollary 
of  parasitism  of  the  latter  type  is  extreme  specialization  in  food  preferences. 
The  series  in  the  fungi  grades  from  violent  and  destructive  parasites  like 
Botrytis,  on  the  one  hand,  to,  on  the  other  hand,  so  benign  an  infestation  as 
the  seed  fungus  of  Lolium  temulentum  (described  by  Freeman,  1903)  in 
which  the  relation  is  so  intimate  and  devoid  of  any  untoward  effect  on  the 
host,  and  the  life  history  of  the  cohabiting  organism  is  so  parallel  with  that 
of  the  grass  that  its  distinct  individuality  is  almost  open  to  question. 

The  mutualistic  nature  of  the  relation  between  host  elements  and 
fungus  in  rusts  of  the  type  of  the  cereal  rusts  is  commented  on  by  Tubeuf 
(1897,  p.  91)  who  very  aptly  compares  the  mass  of  chlorophyll-bearing 
leaf  cells  infested  with  the  rust  mycelium  to  a  lichen  structure,  especially 
to  those  lichens  whose  algae  obtain  water  and  inorganic  materials  direct, 
rather  than  through  the  fungous  hyphae.  Certainly,  during  the  greater 
part  of  the  relation,  there  is  here  no  evidence  of  any  deleterious  effects  on 
the  host  cells.  While  the  contribution  of  the  affected  elements  to  the 
.growth  and  fruiting  economy  of  the  host  plant  as  a  whole  may  be  diminished, 
the  infected  protoplasts  continue  essentially  unimpaired  in  structure  and 
function.  The  parasite  does  not  attack  the  living  substance  of  the  host 
protoplast,  but  confines  itself  to  establishing  such  a  relation  with  the  latter 
that  it  shares  the  available  food  resources  of  the  cell ;  and  the  rust  haustorium 
is  not  an  implement  for  mechanical  disruption,  but  a  structure  more  in  the 
nature  of  the  placenta  of  the  mammalian  foetus  for  establishing  physiological 
communication  with  the  food  resources  of  the  host. 


May,  1922]  RAINES  —  VEGETATIVE   VIGOR  OF   THE   HOST  235 

The  data  presented  by  Thomas  (1921)  on  the  parallel  relation  between 
health  of  the  host  and  infection  in  the  case  of  the  leaf  blight  of  celery,  and 
observations  of  similar  occurrences  in  other  diseases  caused  by  non-obligate 
parasites  like  the  late  blight  of  the  potato  (Jones,  1905)  and  the  crown  gall 
of  the  beet  (Levine,  1921)  indicate  that  phases  in  which  a  symbiotic  tend- 
ency comes  to  the  fore  may  occur  in  diseases  of  a  predominantly  destruc- 
tive type  caused  by  facultative  parasites,  and  suggests  the  generalization 
that  the  host-parasite  relation  in  any  given  instance  is  not  constant  but 
may  vary  with  the  state  and  condition  of  the  organisms  and  with  the  prog- 
ress of  the  relation.  It  is  important  to  recognize  that  there  may  occur 
mutualistic  phases  and  stages  in  host-parasite  relations  of  a  violent  and 
destructive  type,  just  as  there  are  destructive  phases  in  parasitisms  of  a 
predominantly  symbiotic  tendency  such  as  those  of  the  mildews,  the  rusts, 
and  the  smuts. 

CONCLUSION 

The  inquiry  initiated  by  the  occurrence  in  rust  literature  of  statements 
of  a  relation  between  host  vigor  and  susceptibility  other  than  the  inverse 
relation  commonly  conceived  as  existing  between  these  variables  can  be 
considered  as  having  brought  forward  evidence  indicating  that  through 
most  of  the  course  of  certain  infectious  diseases  such  as  the  rust  diseases 
of  the  cereal  grains,  and  in  certain  phases  of  other  diseases  like  the  leaf 
spot  of  celery  and  the  crown  gall  of  the  beet,  the  vegetative  vigor  of  the 
host  and  the  virulence  of  the  disease  may  be  in  direct  relation.  The  demon- 
stration of  such  a  relation  in  diseases  of  large  importance  suggests,  in  turn, 
emendation  of  current  pathological  concepts  of  the  relation  between  host 
vigor  and  pathogen  activity  into  a  form  more  in  accord  with  our  knowledge 
of  parasitological  phenomena  in  general.  A  more  catholic  point  of  view 
in  pathologic  thought,  recognizing  that,  for  longer  or  shorter  phases  in  the 
course  of  a  disease,  the  relation  between  host  and  parasite  may  be  highly 
mutualistic,  would  be  of  material  value  as  a  working  concept  in  the  study 
of  disease  and  in  defining  the  practical  problem  of  disease  prevention  and 
control. 

The  work  presented  in  this  paper  was  done  in  the  Botanical  Laboratory 
of  Columbia  University,  under  Professor  R.  A.  Harper,  to  whom  the  writer 
is  greatly  indebted  for  pointing  out  the  problem  and  for  constant  con- 
sultation and  advice  during  the  progress  of  the  investigations.  Acknowl- 
edgment is  also  made  of  indebtedness  to  Dr.  Michael  Levine  for  taking  the 
photographs  of  the  soil-culture  experiments,  and  to  Dr.  H.  E.  Thomas  for 
helpful  advice  in  devising  the  method  used  in  the  dosage  studies  on  the 
corn  rust. 

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238  AMERICAN   JOURNAL   OF    BOTANY  [Vol.  9 

DESCRIPTION   OF  PLATES 
PLATE  XI 

FIG.  I .  View  of  one  of  the  four  series  of  pots  of  experiment  V  of  the  soil-culture  studies, 
illustrating  the  difference  in  vigor  of  growth  between  plants  receiving  different  nutritive 
treatment. 

FIG.  2.  On  the  left,  a  pot  containing  5  plants  of  group  A  (grown  in  sand) ;  and  on  the 
right  a  pot  containing  5  plants  of  group  F  (soil  highly  fertilized  with  NaNO3) ;  experiment 
V  of  the  soil-culture  studies. 

PLATE  XII 

FIG.  3.  Crown  rust  of  oats.  A  rust  mycelium  exhibiting  a  very  marked  tendency 
towards  teleutospore  production.  The  first  sorus  produced  by  the  mycelium  (in  the  center) 
is  a  uredosorus.  The  others  are  teleutosori.  Photographed  with  Zeiss  3.5  cm.  microplanar. 
X24. 

FIG.  4.  View  of  infected  leaves  of  a  semi-starved  plant  and  of  a  richly  fed  plant  of 
soil-culture  experiment  V,  showing  larger  size  of  pustules  on  more  luxuriant  host  plant. 
Photographed  with  Zeiss  microplanar.  X  15. 

FIG.  5.     Same  as  figure  4.      X  10. 


AMERICAN  JOURNAL  OF  BOTANY. 


IX,  PLATE  xii. 


'\J 


RAINES:   VEGETATIVE  VIGOR  OF  THE  HOST 


VITA 

MORRIS  ABEL  RAINES.  Born  1894.  Elementary  and  high  school 
education  in  the  public  schools  of  New  York  City.  Entered  Columbia  Col- 
lege in  1912.  Received  degree  of  Bachelor  of  Science  "with  high  honors  in 
botany  and  zoology,"  1915;  degree  of  Master  of  Arts  in  1917.  Pulitzer 
Scholar  in  Columbia  University,  1912-1916.  Research  Assistant  in  Botany 
in  Columbia  University,  1916-1917.  Appointed  Gottsberger  Fellow  in  Col- 
umbia University  for  1917-1918,  but  resigned  to  enter  National  Service. 
Flying  Cadet,  and  later  Lieutenant  (airplane  pilot,  rated  "Reserve  Military 
Aviator")  in  the  United  States  Army  Air  Service,  1917-1918.  Instructor 
in  Botany  in  Columbia  University  Summer  Session,  1919.  Gottsberger 
Fellow  in  Columbia  University,  1919-1920.  Instructor  in  botany  in  West 
Virginia  University,  1920-1922. 


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